The state of California and local jurisdictions can encourage safe and legal water reuse which allows the maximization of water’s utility on-site and encourages the treatment of used water prior to discharge.

Responsible sustainable management of global water resources is one of the primary challenges of the 21st century. This is particularly true in California, where source waters and their ecosystems are stressed and degraded due to current management strategies in the face of agricultural needs, population growth, urban sprawl and climate change. California has a history of naturally varying hydrological conditions. It is common for our region to experience short periods of wet weather, followed by extensive periods of drought. In the last 100 years, we have been in a drought for 35 years, roughly one third of the time.[1] Over the past decade, the average early snowpack in the Sierra Nevada, the main source of the state’s water supply, has decreased by about 10%[2].Given the state of water supplies in California, and their corresponding water quality issues, water conservation and water reuse are necessary norms in California at all times, not just during drought periods. Graywater reuse contributes to resource efficiency and sustainable, localized water management. Organizations such as LEED, the International Code Council with “National Green Building Standard,” and The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) with “Standard 189.1-2009 - Standard for the Design of High-Performance Green Buildings” all recognize the use of graywater to satisfy the option for water use reduction. Graywater reuse at the domestic level is one of the simplest forms of water reuse and should be investigated and encouraged as a means to reduce the impact of residential developments on water resources.[3]

Legislative and executive drivers, such as the Clean Water Act, and the various iterations of Energy Policy Acts also point to water reuse as both water and energy sensitive strategies for reduction of demands on our resources.[4] Graywater has the potential to reduce the demand for new water supply, reduce the energy and carbon footprint of water services, and meet a wide range of social and economic needs. In particular, the reuse of graywater can help reduce demand for more costly high-quality potable water.

Historically, in California, graywater systems have been largely unpermitted, ad hoc systems designed by the residential water reusers. Art Ludwig of Oasis Design estimates that there are over 1.7 million illegal graywater systems in California.[5] These systems range from informal bucketing systems that convey water from shower “warm-up” water to laundry to landscape all the way through to systems that gather water from kitchen sinks and dishwashers.

Taking a graduated step towards facilitating residential graywater use, in January 2010, the California Building Standards Commission adopted Title 24, Part 5, Chapter 16A into the California Plumbing Code. The new graywater code (under revision for the 2012 code revision cycle at the time of writing) addresses residential outdoor graywater use.

The 2010 CPC clearly outlines the purpose for the code development: Title 24, Part , Chapter 16A - California Graywater Design Criteria

Chapter 16A establishes minimum requirements for the installation of graywater systems in occupancies regulated by the Department of Housing and Community Development (HCD). It is intended to provide guidance to code users while providing flexibility that will encourage the use of graywater. This part is applicable to occupancies under the authority of the Department of Housing and Community Development as specified in Section and is intended to:

  1. Conserve water by facilitating greater reuse of laundry, shower, lavatory and similar sources of discharge for irrigation and/or indoor use.
  2. Reduce the number of non-compliant graywater systems by making legal compliance easily achievable.
  3. Provide guidance for avoiding potentially unhealthful conditions.
  4. Provide an alternative way to relieve stress on a private sewage disposal system by diverting the graywater.

The code facilitates increased potable water conservation, alleviates stress on residential septic systems, and provides guidelines for avoiding potentially unhealthful conditions.

Graywater from Residential Single Family Unit (RSFU) and Multi-Residential Family Units (MFRU) flows with blackwater to a wastewater treatment plant, which then discharges the treated water to a local waterway. Appropriately matching water quality to water needs graywater reuses water on a local scale supports watershed health through natural water filtration and infiltration processes, while also reducing potable water use. Graywater reuse conserves energy resources as well, negating the energy needed to pump and treat water, decreasing the overall costs for water delivery and treatment, and reducing demand on limited supplies.

Since the 2010 changes to the CA Plumbing Code, more cities and water agencies in CA have promoted and even subsidized graywater systems through rebates, incentives, and public education programs. Public education programs for policy makers, state and local government as well as the public will assist the trend toward incorporating graywater wherever appropriate. Internationally, Australia, Germany, Japan, and the United Kingdom are the current leaders in the use of graywater.[6]


Graywater is defined in various ways around the world. Reviewing other definitions is useful in understanding options for treatment and use of waters, such as kitchen sink effluent, which is disallowed in California. For instance, Canada, Australia, Queensland[7] and Europe define graywater as “(a)ny wash water that has been used in the home, except water from toilets, is called grey water. Dish, shower, sink, and laundry water comprise 50-80% of residential "waste" water. This may be reused for other purposes, especially landscape irrigation.”[8]

“Graywater means untreated wastewater which has not been contaminated by any toilet discharge, has not been affected by infectious, contaminated, or unhealthy bodily wastes, and which does not present a threat from contamination by unhealthful processing, manufacturing, or operating wastes. Graywater includes wastewater from bathtubs, showers, bathroom washbasins, clothes washing machines, and laundry tubs but does not include wastewater from kitchen sinks or dishwashers.” (CA Water Code: SECTION 14875-14877.3)[9]

As per the cited Water Code, in California, “graywater” (also spelled graywater, gray water and grey water) is defined as water that comes from:

  • bathroom sinks,
  • showers/tubs and
  • clothes washing machines.

In California, graywater is not water that comes from a toilet or a kitchen sink. Water used in the kitchen sink is considered graywater in some states, blackwater in others, and dark gray in yet others due to the higher levels of grease, fat, and bacteria found in the water. In California, kitchen sink water is considered blackwater. As such, it’s not a legally allowable source for graywater harvesting.

Graywater is sometimes confused with rainwater (water collected from roofs and other surfaces), which is often stored for later use. Graywater is not rainwater or rainwater’s Janus face, stormwater. As we will later discuss, graywater should never be stored for over 24 hours.

Graywater is also confused with blackwater (aka, sewage). Blackwater is water contaminated with fecal material, such as used toilet water (blackwater) and laundry loads of dirty diapers.

Graywater is also not recycled or reclaimed water, which is water from sewer treatment plants treated to various standards from nonpotable to potable for reuse.

Although graywater usually contains traces of dirt, food, grease, hair, and household cleaning products, it is a safe and even beneficial source of irrigation water, depending on the types of products used in the kitchen and bathroom. Graywater also provides an alternative supply for other non-potable water needs such as toilet flushing and clothes washing.

Graywater is an important component of integrated water management. When used in concert with conservation and efficiency, water wise landscaping, and rainwater harvesting, it can greatly lower potable water demand as well as the need for costly wastewater treatment. Graywater also serves for onsite groundwater replenishment. Graywater is a form of onsite (aka localized) water treatment.[10]

For the purposes of this BMP, we are addressing indoor and outdoor graywater production and use for single and multi-unit residential sectors.


Graywater is a diverse water supply that serves a variety of on-site end uses. Each site must be evaluated to determine the most functional and economic use of graywater in sitio. In general, graywater can be used at the residential scale for all of the following purposes.

Guidelines for using graywater in California

  • Any graywater system that includes a connection to a potable or municipal water supply must have an approved, backflow prevention device. Laundry to landscape graywater irrigation systems that are exempt from permitting must have no connection to the potable water supply or an external pump.
  • The graywater system design must include an accessible, clearly labeled, three-way valve that diverts the graywater back to the building sewer. *Graywater should be diverted to the building sewer during the rainy season between November and April.
  • Any graywater system that includes a connection to a potable or municipal water supply must have an approved, backflow prevention device. *Laundry to landscape graywater irrigation systems that are exempt from permitting must have no connection to the potable water supply or an external pump.
  • The graywater system design must include an accessible, clearly labeled, three-way valve that diverts the graywater back to the building sewer. *Graywater should be diverted to the building sewer during the rainy season between November and April.
  • The graywater must not leave the property where it came from or come within 100 feet of any creek, wetland, or waterway.
  • The groundwater table must be lower than 3 feet from the lowest graywater irrigation or disposal point.
  • Each release point must be covered with at least 2 inches of mulch, rock, soil, or a soil shield. Sprinkler irrigation and ponding of graywater are not allowed!
  • Water used to wash diapers or other infectious garments must be diverted to the building sewer.
  • Graywater may not contain hazardous chemicals.
  • Graywater may not be used to irrigate root crops or other edible crops that touch the soil. 
  • An operations and maintenance manual for the graywater system must be provided by the installer and must be transferred to the new tenant or owner for the life of the graywater system.

Graywater irrigation systems must be located a minimum horizontal distance away from the following landscape features:

Figure 1 Table modified from CA Central Coast Graywater Alliance:

Landscape Feature Minimum Horizontal Distance from Graywater Irrigation System
Building structures 2 feet (610 mm)
Property line adjoining private property 1.5 feet (458 mm)
Water supply wells 100 (30,480 mm)
Streams Rivers, Lakes, Wetlands, and High Tide line of Ocean 100 feet (30,480 mm)
Sewage pits or cesspools 5 (1,524 mm)
Sewage disposal field 4 (1,219 mm)
Septic tank 5 (1,524 mm)
On­ site domestic water service line 0 (0 mm)
Pressurized public water main 10 (3,048 mm)

For detailed information regarding required setbacks for graywater tanks, graywater irrigation fields, and graywater disposal fields, see Table 16A-1 of Title 24, Part 5, Chapter 16A of the California Plumbing Code.[11]

Graywater systems are separated into three categories:

  1. Single Fixture Clothes Washer
    • no permit required
  2. Single System
    • exceeds washer or single fixture system
    • capacity is 250 gallons per day or less
    • construction permit required
  3. Complex System
    • multi family or multi dwelling unit
    • capacity is greater than 250 gallons per day’
    • construction permit required
    • construction Permits
  4. Applies for Small or Complex Systems
    • identify groundwater level and soil type for absorption qualities
    • may use a 3 foot vertical test hole to show groundwater is lower than hole
    • all components must be water tight
    • must be inspected by enforcement agency

Other local regulations and inspection requirements many apply (contact local enforcement agency)[12]

Graywater end uses, outdoor and indoor

Outdoor Use

  • year round irrigation
  • backup irrigation during dry/drought periods
  • year-round groundwater recharge
  • firebreak in dry areas

Graywater is an excellent water source to irrigate plants, trees, and shrubs. Graywater can be used for subsurface irrigation of ornamental plants, fruit trees, and lawns, and is best suited for use with mature plants (not saplings), which have considerable tolerance to salinity, sodium compounds, and high pH levels. It should not be used to irrigate vegetables or fruit-bearing plants if the edible portion may come in contact with the graywater.

The most cost-effective outdoor systems are simple, gravity-driven distribution systems that avoid the need for pumping.[13]

Graywater is also an effective choice for localized groundwater recharge, depending on the level of the groundwater table. It can also provide a firebreak to residential properties.[14]

Indoor Use

  • Toilet flushing
  • Clothes Washing

Given water supply security issues in California, it simply does not make any sense to flush toilets with potable water if flushing with graywater (or rainwater) is a cost-effective option, particularly in new construction, which can be plumbed for dual-plumbing when in construction. Graywater can and should be used for toilet flushing to offset potable water demands.

Issues concerning graywater use for toilet flushing and clothes washing include fixture staining, water discoloration, water quality, safety hazard for children and pets, and odor. It is recommended that graywater be treated to prevent odors and discoloration of flush toilet fixtures, and to address any health-related concerns (e.g., splash back onto sensitive tissues).[15]

Graywater advocates suggest that graywater from the final rinse of a clothes washer cycle can be reused as the first wash water for the next cycle which can then be sent out of the machine onto landscape thus providing three rounds of use for the same water. While this is a viable end use for graywater, technologies are not yet available for this type of reuse.

In 2009, the state of California passed the CA Plumbing Code, Chapter 16, Part A, which determined the legal use of graywater in outdoor residential settings. This code writing process brought new and renewed interest in the use of graywater in California. It also brought to the fore many of the impediments to the use of graywater, many voiced by public health officials and building and permitting departments.

According to Richard Scholze in his 2011 report on graywater for the US Army, the most common controversy and reluctance to graywater use is the potential health threat. However, “(t)here have been no cases reported to the Centers for Disease Control (CDC) related to graywater use.”[16] Most graywater has a low enough concentration of contaminants and disease-causing microorganisms that it can be reused in applications without biological treatment or disinfection as long as the application has a low risk of direct public contact (e.g., subsurface irrigation and toilet or urinal flushing and when storage is not required).

Many of the potential risks to human health and other possible unfavorable side effects of graywater reuse such as encouraging breeding of mosquitoes, etc. can be reduced or eliminated by obviating storage. Also, graywater should be applied at a rate that the soil can absorb it to avoid saturation and pooling.

System Permitting Requirements

Graywater system collects water from showers, sinks, or baths

  • Graywater system alters the plumbing (you cut into the drainage plumbing to access the graywater).
  • Graywater system is installed in a building that is not a one- or two-unit residential building.
  • Graywater system includes a pump (besides the washing machine’s internal pump) or a tank.[17]

Graywater Storage

Most SRUs do not require graywater storage, as the water is being distributed via LTL or branched drain systems to the exterior landscape immediately upon use. If residents use graywater for applications other than subsurface irrigation, such as toilet flushing, the graywater should not be stored unless treated and disinfected, and never for longer than 24 hours. Direct reuse without storage is highly recommended, as it minimizes the problems of microorganism growth and odor.

Should storage be necessary, as in MRUs, the tanks should be sized to empty completely within the first 24 hours after use, so as to alleviate fetid graywater sitting for more than 24 hours at the bottom to inoculate the next batch.[18] Design the system so that all pipes are at a gradient and angle all tank bases so that, if necessary, the entire system can be emptied of water.[19] Left untreated, stored graywater can quickly become septic and develop a population of anaerobic bacteria that will proliferate and create noxious odors.[20]

Considering a Graywater System

The San Francisco Public Utility Commission (SFPUC) has created a useful guide for SRU or MRU residents in how to approach graywater harvesting:

Developing a Graywater System:

  • Start with conservation! Conservation is always the most economical and environmentally beneficial place to begin. You might find that your landscape doesn't require as much water as you've been giving it, or that there are easy ways to greatly reduce the amount of water your household uses. If you are not able install an actual graywater system, you can still reuse water by collecting shower water in a bucket as the water heats up and using it to water your plants.
  • Determine which fixtures in your home are candidates for graywater capture. Washing machines are usually the easiest place to begin. Another potential fixture for graywater capture is the shower and bathtub faucet.
  • Analyze how water drains on your site and find out your soil type with a “soil ribbon test” and/or a low cost laboratory analysis (required if your system needs a permit). In combination with your flow calculations, this analysis will help you determine how large your graywater distribution system will need to be.
  • Read about types of graywater systems and decide which is best for you.
  • Draw a sketch of your proposed system. If a permit is required, you [may need to] submit a plot plan and details about the system to [your city or county’s] Department of Building Inspection.
  • Find an installer or install the system yourself.
  • Remember to label the system (3-way valve and all above-ground graywater pipes) and keep an owner’s manual with it.
  • Operate and maintain your system.[21]


Graywater is beneficial both for residential users, as well as for the environment. Graywater is a purely local water supply -– it is both produced onsite and used onsite as close to the point of production as possible. If graywater harvesting is appropriate for a site, it can provide a substantial quantity of local water for reuse.[22]

“It's a waste to irrigate with great quantities of drinking water when plants thrive on used water containing small bits of compost. Unlike a lot of ecological stopgap measures, grey water reuse is a part of the fundamental solution to many ecological problems…” -- Art Ludwig[23]

Potential Benefits

  • Reduce potable water use by 40-65%, depending on the house/site
  • Reduce water bills due to decrease in potable water use and sewer effluent output
  • Reduce energy and chemicals used to treat the water to potable standards at the wastewater treatment plant
  • Reduce household effluent sent to treatment plant – thereby reducing energy costs to treat and/or reuse water
  • Improve quality of household effluent to waste treatment plant[24]
  • Recover nutrients such as nitrogen and phosphorus
  • Reduce dependency on imported water or local aquifers
  • Improve Soil condition and plant growth with nutrients in the graywater, which can nearly match those of commercial fertilizers
  • Increase groundwater recharge
  • Encourage the use of nontoxic products
  • Connect people to their household water supply as well as to their watershed
  • Alleviate stress on septic systems or treatment plants
  • Provide drought insurance for landscape
  • Provide a fire break and/or greenbelt of high-moisture species
  • Gain LEED and Green Building Rating System pointa
  • Take advantage of federal, state and local rebates and incentives
  • Encourage knowledge of localized water use, treatment and reuse
  • Encourage understanding of hydrologic cycle and local watersheds.

Potential Drawbacks

  • May be more costly
  • May decrease flow return to the sewage plant[25]


The 2009 California Plumbing Code for graywater states that the following are legal residential and multi-residential non-potable graywater systems:

There is a wide range of technologies from simple buckets to complex processes with storage tanks and treatment systems available for reusing graywater in residential and multi-residential contexts.[26] These include:

  • manual bucketing water spent while heating to a desired temperature,
  • direct discharge of graywater from clothes washers, bathroom sinks, showers/baths to the *building exterior for simple infiltration or for landscape irrigation
  • piping bathroom sink graywater into toilet tank reservoirs.

Some systems function without treatment, and others utilize technologies as complex as real treatment plants on a miniature scale. Many systems that a home or multi-unit owner can purchase commercially produce a filtered, disinfected product.

While current technologies around the world support a wide range of graywater sources and uses, not all are legal in California, as previously noted.

Laura Allen makes the point that all manufactured systems use plastic, pumps requiring electricity, maintenance and eventual replacement. If you have plants to water, use untreated greywater outside – you'll save money, time, and energy.[27] That said, graywater is a consistent and relatively readily available source of water, and toilet flushing a regularly needy source, making them well matched. Their practicality and cost effectiveness depends upon advances in technology.

As Art Ludwig points out, it is best to use graywater as close to the source and as soon as possible.[28] This makes graywater a truly local and immediate water source.

Manual Bucketing

Figure 2
Source: Daniel Bowen,

Manual bucketing is a practice that individuals employ to divert water from showers/baths and sinks, often while water is heating up, for non-potable uses. Manual bucketing is also used to capture graywater from a shower or sink after use. Both forms of bucketing are widely practiced and are common and promoted practices in Australia. It is generally not covered by any ordinance or code where it is being encouraged.[29]\\Manually irrigating with greywater using a bucket (e.g. collecting shower and laundry water for reuse) has the potential to reuse small quantities of greywater, thereby saving drinking water. Bucketed greywater can be reused for irrigation of gardens, lawns and outdoor pot plants.[30]

The cost for manual bucketing is minimal based on finding or buying a bucket.

Manual bucketing is not addressed in the CPC 2009, but is encouraged by water agencies, such as the SFPUC.[31]

Direct Discharge

1. Laundry-to-Landscape Laundry to landscape (LTL) graywater systems are one of the most simple and least expensive graywater systems that can be installed in single and multi-residential buildings. In all likelihood, they are the most commonly used system in California, along with manual bucketing.[32] These systems are also relatively inexpensive.[33]

Figure 3
Source: SFPUC,

Laundry-to-Landscape is a washing machine-pressurized irrigation system. The basic concept is to divert graywater by a hose connected to the outlet of the clothes washer, and running this hose to reach the sub-surface irrigation area. Adjustable valves are then added as part of the distribution system to allow the graywater to empty into mulch basins around trees and plants.[34]

Laundry-to-landscape systems generally require no pumping, instead utilizing the washing machine pump and gravity to push the water into the soil through the exterior distribution system. These systems are useful where water is needed for irrigation or where pervious surfaces allow infiltration.

Figure 4
Source: Greywater Corps:

If Laundry to Landscape systems keep working as well as they have so far, most homes should have one. It is a cost-effective retrofit system, and renter-friendly. It can irrigate areas level with or slightly uphill from the washer. This is the system I recommend most often, usually in combination with a Branched Drain or Green Septic system.[35]

Collection potential in laundry to landscape systems varies according to the age and type of the clothes washer, as well as the number of wash loads per month that are appropriate for graywater (i.e. – no harmful chemicals or fecal material). Older top loading clothes washers use approximately 30 to 45 gallons of water per load. High efficiency clothes washers range from 3 to15 gallons of water per load, 12 gallons being more or less typical according to AWWA.[36]. A family of four using a standard sized clothes washer will generate more than approximately 300 loads per year. This equates to a non-efficient washing machine consuming approximately 12,000 gallons of water annually and a high efficiency approximately 3,600 gallons a year.

According to a study by Aquacraft, clothes washers account for 24% of water consumption in a typical household of four people, nearly a quarter of total water use.[37]

Source: Aquacraft and American Water Works Association,

The USGS estimates that a person in California uses 124 gallons a day indoor and outdoor.[38] In Figure 5, Aquacraft estimates clothes washers account for 24% of single-family water use. Accordingly, approximately 30 GPCD is produced. With 37,691,912 people living in the state, 1,130,757,360 gallons or approximately 3470 AF of graywater is produced per day from residential clothes washers in California.

In reality, only some percentage of these nearly 3470 AF gallons that Californians produce in clothes washer use will be appropriate for graywater use, due to loads that include chemicals such as bleach and fabric softeners, as well as materials soiled with feces, reducing the probable total available for graywater.

2. Bathroom Sink, Shower, Bath to Exterior Landscape Graywater can be distributed from the bathroom sink, shower or tub into the landscape, generally through a gravity-fed branched drain system. Graywater drains through a series of branching pipes and is dispersed into the landscape via mulch basin outlets. This system alters the existing plumbing and requires a permit.

Figure 6
Source: Oasis Design,

The case of shower/bath or sink to landscape varies from laundry to landscape in a number of ways, even if the graywater is being diverted to external landscaping or wetlands. This is because, unlike laundry to landscape, diverting graywater from a shower or tub requires cutting into existing plumbing. Depending on the height of the graywater source in relation to the distribution system, gravity may supply the “power supply” for moving graywater; however, it may also be necessary to add a pump. The state of California requires a permit for these types of diversion systems.

System costs can range from a few hundred dollars if installed by homeowner to a few thousand dollars if installed by a professional.[39]

Most simple and complex graywater systems from bathroom sinks, showers/tubs rely on gravity to move water through a branched drain irrigation system.

Graywater from showers, sinks, or laundry is directed to a temporary holding tank and then pumped to the landscape, which can be uphill of the graywater source(s). This system usually alters the existing plumbing and always requires a permit; an additional electrical permit might also be required for the outlet into which the pump is plugged.[40]

According to Figure 5, 36% of residential shower bath and faucet water used is available for graywater.[41]Given the California water use of 124 GPCD, 36% of which is 44.6 GPCD, and with the state population of 37,691,912, this leaves a total of 1,681,059,275 gallons, or 5158 AF available for graywater use. This is again with the caveat that not all of these water sources will be usable for graywater due to contamination from chemicals or feces.

Cost without Pump: Ranges from a few hundred dollars if installed by homeowner to $1,000 to $2,000 if installed by a professional.

Additional Cost with Pump: Ranges from $500-$700 installed by homeowner to a few thousand dollars if installed by a professional.[42]

The California Plumbing Code exempts laundry to landscape systems only from construction permits where no modifications to the plumbing system are required or pumps are used in the graywater system. Systems must still meet the design and construction standards found in the regulations.

3. Clothes Washer, Bathroom Sink, Shower/Bath to Toilet Residents can harvest graywater from shower/bath and sink water directly into a toilet tank for flushing or into a receptacle that is then pumped into a toilet tank. This is very effective use of graywater in a residential building, particularly multi-unit buildings.[43] Graywater provides a continuous supply of harvested water for flushing toilets. The graywater supply can usually meet 100% of residential and multi-unit toilet flushing requirements, as well as being steady and predictable.[44] These systems are both home-designed and commercially available for maximum scalability.

Figure 7
Source: Smart Planet,

There are some technologies, such as AquaCycle®, BRAC, and Aqus™ that have developed “tap to toilet” technologies, but we need more research to verify the ease and functionality in both residential and multi-residential contexts.

However, it is very difficult to install an indoor toilet flushing graywater system in California. In addition to permitting difficulties, the requirements of meeting water quality standards set out in Title 22 standards for blackwater treatment, as well as regular monitoring, is more than most home owners or multi-unit apartment or condo managers can take on.

According to Figure 5, 60% of residential clothes washer, shower, bath and faucet water used is available for graywater use in toilets.[45] [Individual water use of 124 GPCD, and California’s population of 37,691,912, yields a total of 27,907,091,644.8 gallons or 85,643.6 AF available for graywater use for toilet flushing.] This is again with the caveat that not all of these water sources will be usable for graywater due to contamination from chemicals or feces.

In California, these types of systems require permits. Additionally, and prohibitively, graywater from shower, baths and sinks must be treated to standards set in Title 22, Section 60301.230 before its reuse in toilet tanks, the same standards set for the treatment of wastewater and requires near daily water quality testing. For most residential and multi-family contexts, this requirement is a great deterrent to the installation of the systems.[46]

4. Clothes Washer Final-to-First Wash Cycle The rinse water from a previous load can be used to supply the first wash cycle of the next load. This is not yet a widely practiced diversion in the United States and is not addressed in the CPC. However, relevant technologies are under development.

For instance, “Ron George, the chairman of the International Residential Plumbing & Mechanical Code Committee, has designed gray-water systems in two Texas prisons. He says prisons, which often are built in remote locations and depend on well water and septic systems, make especially good candidates for this water-saving approach. His Texas plans captured the final rinse water from the prison’s laundry in holding tanks to supply the washing machines’ first wash cycle.”[47]

The potential quantity of graywater from these types of systems has not yet been documented. This is a very new technology and deserves research and documentation to be considered for use for graywater in California. Cost for these systems is not yet clear.

These systems are not currently covered in the CPC. [48].

Pipe Identification

There is much discussion about the proper color or marking of pipes and any visible piping for graywater. Thus far, the best way to mark graywater remains under dispute. Given that it is “recycled” water (in the sense that it is reused, though most often not to official Title 22 recycled water standards; with the exception of graywater used in toilets, many people have advocated for purple piping), this goes beyond the color of the pipe into the nature and classification of various reused waters, including rainwater, graywater, stormwater and blackwater. After trying various options, in 2009, the CPC adopted this language:

Chapter 16A, Section 1610.0, Valves and Piping reads:

Graywater distribution piping upstream of any connection to an irrigation or disposal valve shall be identified with the words “CAUTION: NON-POTABLE WATER, DO NOT DRINK.” Marking shall be at intervals not to exceed five (5) feet (1,524 mm).[49]

Figure 8
Source: Seton,


Often, the best solution is to design, install, and maintain a system so that the graywater needs no treatment at all. The reason why graywater is being considered in the first place as a substitute for potable water is because it is already relatively clean. Many of the substances contained in graywater are not harmful to plants, and some serve as nutrients for plant growth.

A number of methods of filtration and treatment are available, although the type of treatment required should be determined by the quality of incoming water, the planned end use, and the degree of maintenance the system user desires. In SRUs and MRUs, treatment and filtration is necessary for only certain types of graywater end use. Neither a LTL Simple system nor a bathroom sink, shower/bath top branched drain or mulch basin requires filtration. However, if the graywater is for flushing toilets or moving into drip irrigation systems, filtration and treatment are required. In locations where using kitchen sink and garbage disposal graywater is legal, filtration and treatment are also called for.

In the case of MRUs, where storage is necessary and large amounts of graywater are captured for reuse in toilets, treatment is almost certainly necessary, while even in large complexes, graywater for irrigation should be immediately released into the distribution systems if at all possible, or stored in a holding tank and completely released within 24 hours.

The level of filtration necessary is determined both by the graywater source, as well as its intended end use. Given that California’s graywater code does now allow kitchen sink or dishwasher water to be used for graywater, instead classifying these waters as blackwater, there no need for filtration when graywater is used directly in landscape (with the exception of drip systems). This is because mulch, soil, and plant roots are excellent at providing natural filtration for graywater.

However, if graywater will supply water for a drip irrigation system or for toilet flushing, filtration needs are more extensive. Each graywater and filtration system must be considered according to the site conditions (soil composition, terrain, and water table), source of graywater and use goals.

There are simple questions to ask in determining filtration needs.

  • How much graywater do I produce?
  • What contaminants are present?
  • What is the desired end us and how much do I need?
  • When do I need the graywater for this end use?

Answering these questions will point to the type and size of system to install. The following chart from New Mexico State University speaks to the potential contaminants in various graywater sources, thereby indicating what might need to be filtered out depending on the intended end use.

Figure 9. Water-quality characteristics of selected domestic wastewater[50]

Water Source Characteristics
Automatic Clothes Washer Bleach, Foam, High pH, Hot water, Nitrate, Oil and Grease, Oxygen demand, Phosphate, Salinity, Soaps, Sodium, Suspended solids, and Turbidity
Automatic Dish Washer Bacteria, Foam, Food particles, High pH, Hot water, Odor, Oil and grease, Organic matter, Oxygen demand, Salinity, Soaps, Suspended solids, and Turbidity
Bath tub and shower Bacteria, Hair, Hot water, Odor, Oil and grease, Oxygen demand, Soaps, Suspended solids, and Turbidity
Evaporative Cooler Salinity
Sinks, including kitchen Bacteria, Food particles, Hot water, Odor, Oil and grease, Organic matter, Oxygen demand, Soaps, Suspended solids, and Turbidity
Swimming Pool Chlorine, and Salinity

Source: National Environmental Services Center, [51]

Now that the water source contaminants are defined, the next step is to identify what form of filtration is needed to remove each contaminant, if the end use dictates its removal. It’s important to keep in mind that even in the case of the end goal being groundwater infiltration, that numerous contaminants survive filtration through roots and soil and can still contaminate ground water.[52] This is certainly the case with many pharmaceuticals and other toxins.

The next chart (Figure 10) identifies treatment options for a variety of substances if the end use necessitates removal. The options for filtration include filter systems built specifically for the residence’s needs as well as commercially available graywater filtration systems. SRUs and MRUs will incorporate filters into toilet flushing systems. Those distributing graywater into landscape or wetlands do not need filtration, as the process occurs naturally.

The following systems may include settling tanks, storage tanks, filtration with activated charcoal, cellulose, or ceramic cartridge, and pumps.

Figure 10

Treatment Variable
Aeration Odor, Organic matter, Oxygen demand, and pH
Alum Soaps, and Turbidity
Carbon filtration Odor
Chlorination Bacteria, and Odor
Crop filtration Bacteria, Food particles, Suspended solids, and Turbidity
Crop uptake Nitrate, Phosphate, Soaps, and Sodium
Dilution Hot water, Nitrate, pH, Phosphate, Salinity, and Sodium
Filtration Food particles, Oil and grease, Organic matter, Soaps, Suspended solids, and Turbidity
Flotation,Oil and grease Oil and grease
Hydrogen peroxide Bacteria, and Odor
Lime Bacteria, Odor, and Sodium
Settling Foam, Food particles, Hot water, Organic matter, Oxygen demand, and Suspended solids
Soil filtration Bacteria, Bleach, Chlorine, Foam, Food particles, Organic matter, Oxygen demand, Suspended solids, and Turbidity
Soil uptake Nitrate, Phosphate, Soaps, and Sodium
Storage Storage,"Foam, Food particles, Hot water, Organic matter, Oxygen demand, pH, and Suspended solids [53]

Source: Pacific Institute, [54]

When installing a residential LTL system, pumped by the laundry machine directly into the branched drain water dispersal system, there is virtually no filtration needed, although some system users add a stocking to trap lint. However, stockings are not considered official filters.

In California, all systems that include a filter must be permitted.


A. Laundry to Landscape, Simple System A simple system distributes water from a clothes washer into a nearby mulch basin through a series of linked drip emitters in valve boxes.

Figure 11
Source: Sustainable Water Management Wiki,

Branched Drain

In a branched drain system, graywater from the bathroom sink and/or shower/bath drains through a series of branching pipes and is delivered to mulch basins in the landscape, where soil and plant roots filter the water. Showers, sinks and laundry can individually drain into the landscape, or be collected together into a single branched drain system.

Figure 12
Source: Sustainable Water Management Wiki,

The graywater irrigation zone must be downhill relative to the graywater source to avoid pumping. Branched drain systems are best suited for irrigating trees, bushes, shrubs, and other larger perennial plants.[55]

Figure 13
Source: Lets Go Green,

A branched-drain graywater system divides the flow into smaller and smaller branches. Branched drain systems do not require pumps or filtration, relying instead on a network of pipes and gravity to deliver graywater into the landscape where nearby soil and plants can filter the water. Showers, sinks and laundry can individually drain into the landscape, or be collected together into a single branched drain system.[56]

Drip Irrigation

Graywater systems that filter out particulate matter can direct graywater into a special drip irrigation system. Some systems require the user to manually clean the filter; other more complex systems have automatic filter cleaning built in. Usually designed by an engineering company, these systems filter graywater so it can pass through small emitters used in drip irrigation. Special graywater drip tubing is used. These systems are automated using timers to control irrigation zones. They are also plumbed to take in potable water when there is not enough graywater to irrigate, or to dump excess graywater into the sewer system if there is more graywater than irrigation need.[57]

Pumping, filtration, and backflow prevention increase overall system cost and maintenance, and increase the potential for permitting difficulties.[58]

Treatment Wetlands

Figure 14
Source: Sustainable Sanitation,

Treatment wetlands are graywater systems that divert graywater into treatment wetlands (also called graywater biofiltration systems), which serve as a soil-based filtration system. Graywater from bathtubs, showers, sinks, and washing machines infiltrates the soil filter where it undergoes biological treatment. These diversion systems typically involve some filtration to capture lint, hair, fats, grease, etc. when capturing water from bathroom sources or kitchen sinks.[59] Constructed wetlands can be used to treat graywater destined for the aquifer or a local creek, river, pond, or estuary, or to create backyard wildlife habitat. They can also be incorporated into more complex systems to treat water for toilet flushing.

Graywater system users can avoid the addition of pathogens, bacteria, and non-biodegradable toxins to surface water can be avoided with the biological treatment provided through wetlands, promoting a healthier ecosystem and more sanitary conditions. Investigations over several years document that E. coli concentrations were reduced by over 99% within the soil filter of wetland treatment systems.[60] That said, Graywater Action makes the important point that a residential greywater system should not contain toxins or dangerous pollutants. Avoiding toxic cleaning products is the best way to keep household toxins out of your local ecosystem. Wetlands can remove or render harmless some industrial pollutants, but require constant monitoring and special design. Don't rely on simple backyard wetlands to treat household hazardous waste![61]

Figure 15
Source: Oasis Design, http://

The system can be built for a single household or a group of households, typically at a low cost.”[62] The costs of this form of graywater treatment can vary widely. Treatment wetland systems are therefore a useful option for multi-family housing as a larger amount of graywater can be treated to remove pollutants via infiltration through a constructed system. It should be noted that wetland treatment systems are land-intensive.[63]

The same guidelines that address landscape in general are applicable to constructed wetlands.

4. IRRIGATING WITH GRAYWATER: IMPACTS ON PLANTS AND SOILS  Graywater, like rainwater, can be a naturally beneficial water source for landscape irrigation. The benefits of graywater on plants is also determined by what sorts of chemicals, soaps and additives are in the water from laundry machines, showers and bathroom sinks. Graywater contains many beneficial nutrients, such as nitrogen and phosphorus. The trick with graywater is to produce it responsibly, with an eye towards its end use.

Figure 16
Source: louisa_catlover;

Reusing graywater necessitates that homeowners educate themselves about which ingredients in their personal care and cleaning products are harmful and which are beneficial for the graywaters’ end use, whether irrigation, toilet flushing or clothes washing. 

Ingredients of personal care products and soaps can be beneficial to plants, particularly those that add phosphate and nitrogen, both needed by plants. However, too much phosphate will have a negative impact.[64] The State of California Department of Water Resources identifies specific ingredients to avoid, including:

  • chlorine or bleach
  • peroxygen
  • sodium perborate
  • sodium trypochlorite
  • boron
  • borax
  • petroleum distillate
  • alkylbenzene
  • whiteners
  • softeners
  • enzymatic components[65]

Primary ingredients to avoid are those containing sodium and boron. Sodium perborate and trypochlorite can add excessive amounts of salt to soil, which increases soil alkalinity. Alkalinity can reduce a plant roots’ capacity to take up water, and can therefore dehydrate plants. Labels can lack specific quantities of sodium, so it is useful to know that in general, liquid soaps have less sodium than powdered soaps. Bleaches, disinfectants and germicides, even if from “natural” products, will impact soil health by killing living organisms.[66]

Usually, plants are healthier when the soil is allowed to dry out between irrigations. Therefore, for best results, one should wait until the soil in the root zone is half dried out before re-irrigating.

DO Use Graywater on

  • Alkaline - loving well rooted plants
  • Ornamentals
  • Trees
  • Fruit Trees
  • Food Crops for which the graywater will not come into contact with the edible portion of the plant

DO NOT Use Graywater on

  • Acidic soil-loving plants
  • Seedlings or young plants 

Graywater Irrigation Issues:

  • Graywater and human contact don’t mix. Therefore, any practice that would result in direct contact should be avoided – these include spraying graywater in overhead sprinklers, surface irrigation, pooling, and runoff.
  • Graywater can easily and quickly clog drip systems without proper filtration and regular maintenance. Either remove solid particles from the water (by filtering or settlement) and increase the diameter of the holes in the irrigation pipe. It is recommended that drip irrigation hoses with small outlets not be used for graywater irrigation unless the solid particulates have been removed.
  • Without regular rainfall or soil flushing, minerals such as salts can build up in the soil. With excessive rain, these additional minerals can runoff into natural waterways causing algae bloom.
  • Graywater can add unwanted salts to water tables if the water table is high. 

Maintaining Graywater Irrigation Zones

Flush soil with potable or fresh water periodically during extended periods of no rain in order to disperse minerals, such as salts, from building up.

Check for these issues and adjust graywater output accordingly:

  • Damp and boggy ground hours after irrigation, and reduce graywater output if soil is overdamp surface ponding and run-off of irrigated water, reducing graywater output if necessary.
  • Poor vegetation growth
  • Excessive vegetative growth with reduced fruit
  • Evidence of pests and diseases on plants
  • Unusual odors
  • Clumping of soil
  • Fine sheet of clay covering the surface.


As graywater gains popularity, an increasing number of vendors are offering graywater systems and individual parts such as storage tanks and filters. As previously discussed, in California, SRU graywater systems from a single fixture that discharges to soil, landscaping or treatment wetlands do not call for preassembled systems, but must be designed for the specific home. In the case of MRUs, the same is true. In the case of complex systems, which collect graywater from more than one source or will be used for toilet flushing, a commercially available system will be appropriate.

There has been little research on the viability and cost effectiveness of these systems. Most of the available feedback is word of mouth that is unsubstantiated by data. Buyers are encouraged to do additional feasibility investigation and research.

The Alliance for Water Efficiency has identified a number of vendors in North America that are promoting systems. This list reviews complete systems, and does not include companies selling individual graywater system parts.[67]


AquaCycle® by PONTOS®, independent subsidiary of Hansgrohe AG, Schiltach, Germany

  • Recycles graywater from lavatory sink, shower, tub and laundry for use in toilet flushing, clothes washing, cleaning, and on landscape
  • Numerous existing installations in small and large residential and institutional applications
  • Company contact (from North America): 011-49-7836-51 19 20

Aqus™ Water Reuse System by WaterSaver Technologies, Louisville, KY

  • Recycles graywater from lavatory sink for use in toilet flushing
  • UPC (Uniform Plumbing Code) listed product
  • Production and deliveries began in 2006
  • Company contact: 502-741-1859

BRAC Greywater Recycling System by BRAC Systems, Montreal Quebec

  • Recycles graywater from lavatory sink, shower, tub, and laundry for use in toilet flushing
  • UPC (Uniform Plumbing Code) listed product
  • In production

UTrial underway in Seattle

  • Company contact: 866-494-2722 or 514-856-2722

Ecoplay, Muiden, The Netherlands

  • Recycles graywater from shower and tub for use in toilet flushing
  • Company contact (from North America): 011-31-294-26 43 11
  • Not readily available in the U.S. at this time

Econocycle: ultraGTS Domestic, Silverdale, New South Wales

  • Captures and recycles graywater from lavatory sink, shower, tub, and laundry for use in toilet flushing, landscape irrigation, and general cleaning
  • System not yet available in North America
  • Company contact (from North America): 011-02-4774-1256

Perpetual Water, Phillip ACT 2606 Australia

  • Captures and recycles graywater from lavatory sink, shower, tub, and laundry for use in toilet flushing, landscape irrigation, and general cleaning
  • System not yet available in North America
  • Company contact (from North America): 011-61-2-6162-0650

ReWater by ReWater Systems, Inc., Chula Vista CA

  • Captures, filters and reuses shower, tub, lavatory sink, and laundry water for landscape irrigation
  • Available since 1990; numerous existing installations with proven track record
  • Company contact: 619-421-9121


Residential Water Use

The first question to answer is how much graywater is available for reuse in any specific household, and over the course of a year. The USGS estimates that a person in California uses 124 GPCD indoor and outdoor[68] or 45260 CPCY; this equates to a four-person household using approximately 181,040 gallons of water each year including toilet flushing and kitchen sinks, which is not legally available for graywater reuse in California.

By utilizing graywater reuse systems, a family can capture the water used for bathing and clothes washing, and use it for toilet flushing while the remaining 33% can be used to irrigate the yard.[69] Recycling gray water thus saves fresh potable water for other uses, reduces the volume of wastewater going to septic systems and wastewater treatment plants, and increases infrastructure capacity for new users.[70] According to the AWWA Research Foundation, homes with access to alternative sources of irrigation reduce their water bills by as much as 25 percent.[71]

Given that most households spend a minimum of 50% of their potable water on landscape irrigation, reducing potable water use by using graywater is a good answer to unnecessary potable water use in landscape.[72] This number will vary somewhat depending on the household, the water efficiency of the fixtures and the total area of landscaping. According to numerous sources, such as the University of Arizona[73] and the University of New Mexico[74], approximately 65% of indoor residential water use could be recycled as graywater. Individual households can map water use according to water bill information as well, dividing over all water use by number of residents.

Irrigation efficiency is an important factor. Graywater can comprise a significant portion of the water use at an individual use site—a home, an apartment, or a commercial enterprise—accounting for as much as 50% of the indoor potable water use and meeting about half of the demand for outdoor irrigation use during the irrigation season.[75]

Figure 17 Division of residential water use by category
Source: American Water Works Association (AWWA),

Water footprint tools can also give general average estimates of a specific SRU or MRU resident's water use. A SRU or MRU can also have a professional water audit company perform an onsite water audit. Additionally, there are also specific onsite water measurement tactics that any household residents can employ to determine their specific water use and what amount of graywater is available from showers, baths, bathroom sinks, and clothes washers.

Offsetting Potable Water Use with Graywater

The second determination to make is how much of the potable water use could be offset with graywater produced on site. In order to determine the overall potential for offsetting potable water use with graywater, it is necessary to know how much water is used in landscaping, toilet flushing, clothes washing, which are the current primary uses for graywater.

The following chart divides US average water residential water use by category. (Note that kitchen, bathroom and utility sinks are not broken down individually, so that some of the faucet water used in kitchen sinks is actually blackwater and not available for reuse.)

Figure 18: Maximum Graywater Generation rates in typical U.S. Households[76]

Research on Potential Savings

At the UCLA Institute of Environment and Sustainability, Professor Yorem Cohen Ph.D. has been conducting research in graywater as a potential source of water. He is founder and Director of the Water Technology Research Center at UCLA and provides valuable information on the water savings potential of using graywater. Professor Yorem’s research follows that in order to assess the potential for potable water savings in the residential sector, it is useful to consider three tiers of graywater reuse and how these can be matched with water demand. More specifically, tier 1 includes laundry water, tier 2 includes the first tier and adds to it shower water, and tier 3 includes the first two tiers then adds to it dishwasher and faucet water. Tiers 1 and 2 are considered light graywater (i.e. wastewater from the shower, bath, bathroom sink, and clothes washing machine) while tier 3 is considered heavy graywater (i.e. wastewater from the kitchen sink and dishwasher). It is clear from Dr. Yorem’s research that recycling all of Tier 1 and Tier 2 graywater would be sufficient to meet outdoor water use in Southern California. If heavy graywater were also used, this would meet up to 41% of toilet water use provided this heavy graywater underwent treatment before use. Therefore, the estimated residential per capita potable water savings range would be wide but also quite significant at 16% - 40% for Tiers 1-3.[77]

Another example of residential water use in South Coast Hydrologic Region of California indicates that a total savings of 2,400 MGD would depend on the level of public participation in adopting graywater recycling and reuse practices at the single-residential and community-levels. For example, with a participation of only 10% for tiers 1-3, the potable water savings for the South Coast Hydrologic Region would range from about 40 to 100 MGD (1.6% - 4%). Although the percentile savings may seem small, it is important to note that the volume of water saved is equivalent to, and in some cases larger than, the capacity of a large and modern seawater desalination plant such as those now being proposed for California. Additionally, graywater reuse at the location-of-use has the potential advantage of a lower cost than would be expected for centralized graywater treatment and distribution systems.[78]

Cost Effectiveness

Most homeowners install graywater systems to preserve landscaping where water rationing is prevalent. Other reasons include avoiding fines or environmental stewardship. The cost-effectiveness of graywater systems varies widely, depending on the sophistication of the system, cost of potable water saved, and cost of labor. Studies show that graywater systems with disinfection and an electrochemical treatment step can result in significant cost savings for homeowners and industry.[79] In contrast however, a City of Los Angeles Office of Water Reclamation pilot study metered the graywater diversion and concluded that the amount of water saved in six (of the eight) residential sites over a 12-month period ranged from 2.2 to 11% of the total water use at the sites. Even the simplest system could not have been cost-effective based only on the value of water saved. The California Department of Water Resources at three disparate sites conducted another pilot study and the costs of the systems installed far exceeded the value of the 20-year water savings.[80] A simple benefit–cost analysis (Figure 19 below) indicates that the monetary benefits alone did not justify the costs of these three systems.

Figure 19 Benefit – Cost analysis from three sites in California[81]
Source: Bahman Sheikh.


There may be controversy and reluctance in some areas to use graywater. The most common concern is the potential health threat. However, most graywater is expected to have a low enough concentration of contaminants and disease-causing microorganisms that it can be reused in applications without biological treatment or disinfection as long as the application has a low risk of direct public contact (e.g., subsurface irrigation and toilet or urinal flushing and when storage is not required). The only form of graywater treatment typically provided in these cases is sedimentation to remove coarse solids and grit, and coarse filtration to remove hair and lint. If there is a need to store the water, a more advanced level of treatment and disinfection is required. However, there have been no cases reported to the Centers for Disease Control (CDC) related to graywater use.”[82]

No cases of any disease have been documented through exposure to graywater -although systematic research on this public health issue is virtually nonexistent.[83]

Many research studies on the safety of graywater reuse have been conducted and most agree that graywater is not safe to ingest. Graywater should therefore remain in pipes and be delivered to plants and trees underground. To date there are no documented cases of illness transmitted from graywater reuse in the Untied States.[84] Proper reuse of graywater should not create serious health concerns to the public; however, graywater does include common contaminants such as salts, bacteria, food, household detergents and chemicals, and other microbes that can potentially cause illness. In small amounts, urine and feces is occasionally measured in graywater that was used to wash linens and cloth diapers.[85] Fecal contamination in graywater provides and indication that etiological agents causing infection to humans may be present. The etiological agents include: bacteria, campylobacteria, salmonella, viruses and protozoas such as cryptosporidium and giarida.[86] So while there is no reason for serious health concerns posed from graywater reuse, having a good knowledge of graywater systems is highly recommended.

The most common use of residential graywater is landscape irrigation; therefore users of graywater must understand the health risks and environmental impacts associated with reusing graywater to irrigate their plants and trees. An understanding of how to design use and maintain a graywater system is also very important because not doing so can have negative public health and environmental impacts.[87]

Graywater contains significant amounts of nutrients (Figure 20 below), particularly nitrogen and phosphorus and an average volume of graywater being 356 L per day will produce approximately 45 g of nitrogen and 3 g of phosphorus per day [6].

Source: Jeppersen & Solley,

Perceived Risks

Depending on what specific source of graywater is used and how it is used, the health risks of doing so will vary. For example, careful planning, construction and use will greatly decrease the likelihood of illness. In general, rinse water from the laundry constitutes a lower health risk than graywater originating from common kitchen uses that is of a higher risk. Graywater can be used with a low risk on trees and ornamental plants; however, using graywater in vegetable gardens is considered high risk because direct contamination can occur.[88] Additionally, doing one or more of the following can minimize risks:

  • Do not use sprinklers to distribute graywater, as they create airborne aerosol droplets that can land on edibles
  • Do not use graywater on food plants that are consumed raw
  • Ensure graywater runoff is eliminated
  • Do not irrigate with graywater during wet weather as increased contamination may occur; Use cleaning products that are environmentally friendly such as low-salt liquid products; Alternate graywater use with other sources, such as rainwater and the potable supply;
  • Ensure that graywater does not pool-up by utilizing mulching drain fields, not applying to saturated soils, and applying graywater intermittently so that it properly soaks in;
  • To avoid contamination of the groundwater do not irrigate too close to wells. The proper distance will be regulated by county laws and will vary.

A septic tank and/or leach-field will help in this regard.[89] [90]

Real Risks

While graywater use normally does not carry with it a high risk of infection or illness, precautions must still be taken. A great deal of research has been carried out to determine various contaminant levels. One five-year study was carried out by a team of researchers from Monash University and the University of Melbourne and was funded by the Victorian Smart Water Fund and Water Quality Research of Australia. Conclusions from the Monash research published in October of 2011 indicate that the risks of gastrointestinal illnesses associated with household use of graywater are likely to be very low.[91] While this is good news, another study carried out by the South African Water Research Commission (WRC) in 2011 identifies various health risks from graywater use. The WRC study highlights concerns about human health, which could be threatened in the process of using graywater for food production. This is due to the fact that graywater contains microorganisms capable of causing disease in those who come in contact with graywater or with plants and crops irrigated with graywater.[92]

Figure 21
South African Water Research Foundation,

As noted earlier, fecal matter is detected in clothes and the potential exists for infection from exposure. There has been a lot of study on how much fecal matter is in graywater using the indicator bacteria called fecal coliform bacteria; however, this indicator bacterium often reproduces in graywater and does not measure actual fecal matter. While the most widely used indicator bacteria are members of the coliform group, the enterococci, bacteriophages and spores of sulfite-reducing anaerobic bacteria are now frequently used as well. A more expensive testing alternative uses the chemical biomarker, Coprostanol, which is derived from cholesterol in the gut and does not reproduce in graywater. Study results using Coprostanol were compared to results from a study that used the fecal indicator bacteria and it was shown that the fecal indicator bacteria overestimated fecal matter levels between 100-1000 times more than Coprostanol showed. This strongly indicates that the more common use of the fecal indicator bacteria in testing could be overestimating the severity of contamination by a wide margin.[93] This is an area of further testing that may indeed lead to more accurate data in fecal contamination of graywater. Summaries of research case studies on this topic can be found at


The state of California's recognition of the potential benefit of graywater recycling and its importance in the State's overall water plan is a key step forward. In implementing this approach, California can benefit from the experience that other countries have had with graywater recycling. 

In Australia, for example, government-provided information and certification regarding commercial graywater systems is clear and posted on government web sites. In addition, detailed information is provided to the public sector on available and acceptable graywater recycling technologies and approaches.[94] Moreover, the Australian government has established a National Rainwater and Greywater (NRG) Initiative with funding and rebates to promote efficient and safe graywater recycling and rainwater storage and is available to the entire country.[95] The NRG was launched under the larger Water for the Future initiative. Highlights of the NRG included rebates of up to $500 to households for the purchase and installation of a new rainwater tank(s) connected to the toilet and/or laundry by a licensed plumber; OR the purchase and installation of a graywater system that was installed by a licensed plumber. The NRG also offered grants to surf/life saving clubs of up to $10,000 to: install rainwater tanks; to undertake larger water saving projects; or to conduct water efficiency audits.[96]

Like Australia, Southern California can develop a more sustainable water program by increasing graywater recycling to a level at which it becomes a measurable part of the state's water portfolio. However, an effective graywater recycling program must include broad public education and participation, certified and properly managed distributed graywater recycling systems, centralized recycling plants where applicable, and incentives for graywater recycling programs.[97]

Selected Rebate programs in California

San Francisco Public Utilities Commission (SFPUC): Graywater projects that require a permit from the Department of Building Inspection (required for all other graywater systems except laundry-to-landscape), SFPUC offers a rebate up to $225 towards the cost of a graywater permit. The permit rebate will help cover the cost of obtaining a permit from the Department of Building Inspection for your site-specific graywater system. The rebate is available for residential graywater systems with subsurface irrigation. Applications for the rebate can be found at:[98]

Soquel Creek Water District: A $75 rebate is available for each qualified graywater system installed for up to three connections for a maximum rebate of $225. This rebate policy is effective as of July 1, 2010. The three types of connections eligible for rebates include: clothes washing machine or "laundry to landscape" - $75; bathtub and/or shower - $75; bathroom sink - $75. More information can be found at:[99]

City of Santa Rosa: There are two options for the graywater rebate in Santa Rosa. First there is a per fixture rebate at $75 per qualifying fixture that reroutes graywater. The type of system that would typically qualify for this option is the single-fixture or clothes washing machine graywater system. The other option is a sustained reduction rebate at $200 for every 1,000 gallons of sustained reduction in monthly water consumption. The rebate amount cannot exceed the cost of the system excluding labor. This option is typically used for engineered graywater systems. More information can be found at[100]

East Bay Municipal Utility District (EBMUD): Offers customized incentives for permitted graywater systems through the WaterSmart program; however, a permit may be required for certain graywater systems so EBMUD suggests checking with your local building department. To learn more about how to qualify for WaterSmart rebates please visit[101]

The State of Arizona

Arizona passed a law in 2005 that provided a tax credit for the installation of a residential graywater system. The window for the tax credit began in 2007 and expired in 2011. The tax credit equaled 25% of the cost of installing a graywater system and was not to exceed $1000. The credit applied to the full cost of installing the system. The credit was also available to the corporate sector and was applied to the cost of installing plumbing stub outs for a separate graywater system in a residence constructed by a corporation. The corporate tax credit was not to exceed $200 per residence.

The total amount of the credit that was available to all Arizona individual taxpayers was limited to $250,000 per year and only one credit in a tax year is allowed per residence. Tax credits claimed over multiple years by a taxpayer for the same residence were not to exceed $1000. For corporate tax credits, the total amount available was limited to $500,000 per year.[102]


It is common belief in the field that most existing graywater systems are operating without the benefit of a permit. Of the many systems in use in California, only about 200 are estimated to be operating with a permit, about 0.01% of the total.

Between 30 of the 50 states have regulations allowing, prohibiting, or regulating graywater reuse in one form or another. Several other states such as North Carolina allow graywater reuse only if it is first treated to standards identical to those required for the combined wastewater stream.[103]

Definition of Graywater in California

Untreated household waste that has not come into contact with toilet waste. Graywater includes used water from bathtubs, showers, bathroom washbasins and water from clothes washing machines and laundry tubs. It does not include wastewater from kitchen sinks, dishwashers or laundry water from soiled diapers.

The last sentence in the given definition is important as it a revision made in the 2007 California Plumbing Code definition of graywater which states that heavy graywater (i.e. water form the dishwasher and kitchen faucet) must be conveyed and treated at a centralized location such as blackwater. Additionally, the revised 2007 California Plumbing Code has eased previous permit requirements for certain untreated graywater delivery and distribution systems. Permit requirements are now based on daily discharge volume, number of household sources, and number of graywater system fixtures.[104]

In February 2008, state senator Alan Lowenthal introduced SB-1258 (Building standards: graywater), which instructed the Department of Housing and Community Development to adopt revised standards for construction of systems for indoor and outdoor use of graywater. The bill was passed by the legislature and approved by the governor July 22, 2008. The California Department of Housing and Community Development (HCD) then initiated a consultation process with the stakeholders to develop a revised section (Chapter 16-A of the California Plumbing Code) for graywater. Based on the testimony presented at public forums and after several cycles of revisions and extensive comments, the final code language was adopted as an emergency measure by the Building Standards Commission and became effective on August 4, 2009.[105] The code specifically states that, “a graywater system, utilizing only a single domestic clothes washing machine in a one or two family dwelling, in compliance with all of the following, may be installed or altered without a construction permit.” The specific State requirements in California for graywater systems are extracted from the 2010 California Plumbing Code and listed below:[106]

1. If required, notification has been provided to the Enforcing Agency regarding the proposed location and installation of a graywater irrigation or disposal system.
2. The design shall allow the user to direct the flow to an irrigation or disposal field, or the building sewer. The direction control of the graywater shall be clearly labeled and readily accessible to the user.
3. The installation, change, alteration or repair of the system does not include a potable water connection or a pump and does not affect other buildings, plumbing, electrical or mechanical components including structural features, egress, fire-life safety, sanitation, potable water supply piping or accessibility.
4. The graywater shall be contained on the site where it is generated.
5. Graywater shall be directed to and contained within an irrigation or disposal field.
6. Pooling or runoff is prohibited and shall be considered a nuisance.
7. Graywater may be released above the ground surface provided at least two (2) inches of mulch, rock, soil, or a solid shield covers the release point. Other methods that provide equivalent separation are also acceptable.
8 Graywater systems shall be designed to minimize contact with humans and domestic pets.
9. Water used to wash diapers or similarly soiled or infectious garments shall not be used and shall be diverted to the building sewer.
10. Graywater shall not contain hazardous chemicals derived from activities such as cleaning car parts, washing greasy or oily rags, or disposing of waste solutions from home photo labs or similar hobbyist or home occupational activities.
11. Exemption from construction permit requirements of this code shall not be deemed to grant authorization for any graywater system to be installed in a manner that violates other provisions of this code or any other laws or ordinances of the Enforcing Agency.
12. An operation and maintenance manual shall be provided. Directions shall indicate the manual is to remain with the building throughout the life of the system and indicate that upon change of ownership or occupancy, the new owner or tenant shall be notified that the structure contains a graywater system.

Snapshot of Graywater Regulation in Texas:

The Texas Health and Safety Code Graywater Standards

1. The commission by rule shall adopt and implement minimum standards for the use and reuse of graywater.
2. The standards adopted by the commission must assure that the use of graywater is not a nuisance and does not damage the quality of surface water and groundwater.
3. The commission may not require a permit for the domestic use of less than 400 gallons of graywater each day.
4. Each builder is encouraged to install plumbing in new housing in a manner that provides the capacity to collect graywater from all allowable sources; and design and install a subsurface graywater system around the foundation of new housing in a way that minimizes foundation movement or cracking.
5. Graywater is defined as wastewater from clothes-washing machines, showers, bathtubs, hand-washing lavatories, and sinks that are not used for disposal of hazardous or toxic ingredients. The term does not include wastewater that has come in contact with toilet waste; from the washing of material, including diapers, soiled with human excreta; or from sinks used for food preparation or disposal.[107]

Snapshot of Graywater Regulation in Arizona

The State of Arizona law R18-9-711 on reclaimed water general permit for graywater follows that:[108]

1. The Reclaimed Water General Permit allows private residential direct reuse of graywater for a flow of less than 400 gallons per day if specific conditions are met.
2. The following are prohibited: graywater use for purposes other than irrigation, and spray irrigation.
3. Towns, cities, or counties may further limit the use of graywater by additional rule or ordinance.

Snapshot of Regulation in Australia

The Code of Practice for the Reuse of Greywater in Western Australia, has been endorsed by the by the Executive Director Public Health in accordance with Section 344A (2) of the Health Act 1911. More specifically, the Code of Practice sets the minimum requirements for the reuse of greywater systems in western Australia.

Minimum requirements are set on: single residential domestic premises; multiple dwellings producing up to 5000 L/day (1,320 gal) of greywater and; commercial premises reusing up to 5000 L/day.[109]

Snapshot of Regulation in New South Wales (NSW), Australia

The Department of Water and Energy (DWE) of NSW provides the guidelines for allowable reuse of greywater. Approved methods include:[110]

1. Manual bucketing where small quantities of water are collected from either the washing machine or the shower in a bucket for reuse outside on gardens or lawns;
2. Greywater diversion devices which involve the installation of a greywater diversion device to redirect greywater to the garden or lawn via a sub-surface irrigation system. Council approval is not required if the conditions of Section 75A of the Local Government (General) Regulation 2005 are met.
3. Greywater treatment systems in order to reuse treated greywater from toilets and washing machines for use on gardens and lawns. Council approval and a licensed plumber is required to install the system.

For permits, local council approval is required before installing a graywater system. However, a graywater system may be carried out without prior council approval if certain requirements are met. These requirements vary based on local council and water authority. Furthermore, a local council must not approve the installation of a graywater system unless the New South Wales Health department has accredited it. A licensed plumber must also be contracted to install the graywater system and any associated distribution system (e.g. irrigation system, third pipe for toilet flushing).[111]


The importance of graywater recycling and reuse has been recognized by California’s Department of Housing and Community Development which proposed the adoption of emergency graywater regulations into the 2007 California Plumbing Code. Approved by the California Building Standards Commission in August 2009, the revised plumbing code now presents clearer and less restrictive regulations for graywater reuse.[112]

According to the California State Plumbing Code, California doesn’t require permits for those laundry systems not altering household plumbing (often referred to as "laundry to landscape" systems, see diagram below), but does require them for other types of systems in which plumbing must be altered, such as graywater from showers, tubs, and bathroom sinks.[113]

Figure 22: Laundry-to-Landscape graywater system
Source: San Francisco Water Laundry-to-Landscape Pilot Program.,

For new construction and remodels requiring permits, people usually work with their local building department to obtain a graywater permit, or install a graywater stubout to which a future graywater system can be connected after the final inspection. Arizona, Texas, and New Mexico do not require permits for residential graywater, as long as health and safety guidelines are followed.[114]


The California Green Building Standards Code (CALGreen) is the first statewide green building code in the country and seeks to establish minimum green building standards for the majority of residential and commercial new construction projects across California. The 2010 California Green Building Standards Code, or CALGreen, is now mandatory, effective as of Jan. 1, 2011. California is the first state to adopt a green building code that imposes energy efficiency and other green standards on new construction in an effort to achieve reductions in natural resource consumption and greenhouse gas emissions. Despite its first-in-the-nation status, CALGreen represents only a modest change from prior California green building requirements.

CALGreen establishes minimum uniform standards for green building that apply to many types of new construction, including commercial, low-rise residential, state owned and educational buildings. Cities and counties were required to draft and approve ordinances to adopt CALGreen by Jan. 1.

CALGreen was developed by the California Building Standards Commission, the state agency charged with developing and adopting building standards and codes, in response to California’s Global Warming Solutions Act or AB 32. The Act requires a reduction of greenhouse gas emissions levels to those found in the year 1990 by 2020. Following passage of the Act in 2006, state legislators focused on buildings, which are the second largest contributor to greenhouse gas emissions at 24 percent, and introduced several bills containing potentially inconsistent and unrealistic green building standards.

The commission determined that although some cities had implemented green building provisions, the local green building codes were based on different standards, creating inconsistencies from city to city.

In response, the commission sought to set minimum uniform standards. It solicited input from the building industry including the American Architects Association, the Building Industry Association, the International Council of Shopping Centers, the National Association of Industrial and Office Parks, and the California Business Properties Association, as well as state agencies, such as the California Energy Commission, the Air Resources Board, the Department of Water Resources, the Department of General Services, and California Department of Resources Recycling and Recovery. The commission also reviewed LEED and other green building rating systems.

CALGreen encompasses residential and non-residential mandatory measures. The non-residential mandatory measures are classified into the following categories: Planning and Design; Energy Efficiency; Water Efficiency and Conservation; Material Conservation and Resource Efficiency; and Environmental Quality.

In many cases, CALGreen merely adopts existing state requirements. For example, it does not impose any new energy efficiency standards. Buildings are merely required to comply with the California Energy Commission’s existing Title 24 requirements. However, the commissioning requirement is new: a third party must review, test and adjust building design, construction and operation systems to ensure that the components perform according to the developer’s requirements.

CALGreen permits local jurisdictions to adopt codes with requirements that exceed the minimum standards. In addition, CALGreen includes two sets of voluntary provisions referred to as Tier 1 and Tier 2 to encourage communities to take further action. Examples of the Tier 1 voluntary measures include exceeding energy efficiency by 15 percent, achieving 30 percent water savings, reducing construction waste by 65 percent, using up to 10 percent recycled materials, and designating 10 percent of parking spaces for fuel-efficient vehicles.

The Tier 2 voluntary measures are even “greener.” Tier 2 voluntary measures include exceeding energy efficiency by 30 percent, achieving 35 percent of water savings, reducing construction waste by 80 percent, using 15 percent recycled materials, and designating 12 percent of parking spaces for fuel efficient vehicles. Tier 2 also contains a solar reflectance index standard for “cool” roofs.

1. a) Worksheets Water Use Calculation Forms (Section 4.303) WS 1 – Baseline Water Use — (Adobe PDF) or (Microsoft Word) WS 2 – 20 Percent Reduction Water Use Calculation Table — (Adobe PDF) or (Microsoft Word)

  • Provide water efficient landscape irrigation design that eliminates the use of potable water beyond the initial requirements for plant installation and establishment. There is a list of 6 different methods that include plant coefficient, irrigation efficiency and distribution uniformity, use of captured rainwater, use of recycled water, use of graywater, etc.
  • Restore all landscape areas disturbed during construction by planting with local adaptive and/or non-invasive vegetation.
  • On previously developed or graded sites, restore or protect at least 50% of the site area with adaptive and/or non-invasive vegetation.
  • Install a graywater collection system for onsite subsurface irrigation per Appendix G, 2007 California Plumbing Code.

With respect to water use efficiency, CALGreen has mandatory and voluntary measures for residential and non-residential buildings. The goal of indoor residential measures is to reduce potable water consumption by 20%. Mandating the maximum allowable water use per plumbing fixture does this, e.g., 1.6 gallons per flush toilets or 2.5 gallons per minute for a showerhead. For outdoor water use automatic irrigation controllers must be weather or soil-moisture based that automatically adjust irrigation in response to changes in plants’ needs as weather conditions change. Voluntary measures include water efficient clothes and dishwashers and outdoor drip irrigation.

For non-residential building, the mandatory building code is clear: add more meters (aka sub-meters) to measure irrigation use, building use, and so on. Use of graywater and recycled water is also recommended plus measures to reduce blackwater production. Voluntary measures include using native plants.

However CALGreen does not address two key “fixes” that can significantly reduce water waste: improving plumbing and automatic water monitoring. We are all aware of the amount of water we waste everyday waiting for it to heat up. Let’s fix that by mandating building codes that require plumbing upgrades for new buildings that eliminate this huge source of unnecessary waste. Automatic water monitoring identifies leaks and provides insight into water usage and opportunities for conservation. Cost effective and non-disruptive water automation is now finally available (Aquacue Barnacle). Let’s start using this technology to reduce water waste.

The Department of Water Resources and the Department of Housing and Community Development regulate Graywater systems in California. Building codes in the state of California vary depending on different types of construction from residential to commercial. The California building standards codes are set forth under the CALGreen state program by the California Building Standards Commission (CBSC).

With regards to graywater regulations and codes, the CALGreen 2010 report states that non-residential buildings are required to reduce wastewater by 20% and approved graywater systems are suggested in order to achieve this. With respect to residential water use, graywater is approved as an irrigation method in order to either reduce or eliminate potable water use.[115]


The United States Green Building Council (USGBC) provides rating systems for new home construction, current buildings, commercial buildings, schools, retail, etc. These ratings are set forth by the LEED certification system and codes for graywater regulate what must be done in order for a building to receive LEED certification. Graywater systems are included on the “LEED for homes” checklist under the water reuse section; however, this kind of reuse system garners the lowest point total among the three approved reuse systems. Rainwater harvesting and using municipally recycled water score the highest in the water reuse section of the LEED checklist.[116]

LEED rating systems indicate that a graywater system must include a tank or dosing basin that can be used as part of the irrigation system. Graywater must be collected from at least one of the following: clothes washer, showers, or some combination of faucets and other sources estimated to exceed 5,000 gallons per year. Furthermore, a graywater reuse system should be integrated with resource-efficient landscape and irrigation system design. If a home is already using a municipal recycled water system, the home can have but cannot receive points for a graywater reuse system.[117]

LEED rating systems also offer points if education on operation and maintenance of installed graywater systems is provided to the homeowner or tenant. This is also true should education be offered to the building manager.[118]

On average, a LEED certified building uses 30% less water than a conventional building, which translates to more than 1 million gallons of water saved per year. Reducing the amount of water that needs to be conveyed to and treated by municipal wastewater treatment facilities also reduces pumping and process energy required to these systems. LEED, through practices like rainwater harvesting, promotes on-site storage and use of rainwater and graywater to lower water consumption cost, and it reduces the impact on storm drainage and municipal treatment systems. Specifically, water harvesting efforts can earn a significant number of LEED points across several categories:

2. a) LEED Points for Water Harvesting Efforts

  • Stormwater Design: Quantity Control - 1 point (SS Credit 6.1)

Reduce impervious cover, increase on-site infiltration, reduce pollution from stormwater runoff by eliminating contaminants

  • Stormwater Design: Quality Control - 1 point. (SS Credit 6.2)

Storm water treatment systems designed to remove 80% of the average annual post-development total suspended solids using rainwater recycling, vegetated roofs and swales, pervious pavement.

  • Water Use Reduction: 20% Reduction - 1 point. (WE Credit Prerequisite 1) 20% reduction in water use for building using alternative on-site sources of water such as rainwater, stormwater and graywater
  • Water Efficient Landscaping, Reduce by 50% - 2 points. (WE Credit 1.1) Limit or eliminate the use of potable water for landscape irrigation by using captured rainwater, recycled wastewater, groundwater and other means.
  • Water Efficient Landscaping, No Potable Water Use or No Irrigation - 2 points in addition to WE Credit 1.1. (WE Credit 1.2)

Use only captured rainwater, recycled wastewater or recycled graywater for site irrigation.

  • Innovative Wastewater Technologies – 2 points (WE Credit 2)

Reduce generation of wastewater & potable water demand, while increasing the local aquifer recharge – use captured rainwater or recycled graywater to flush toilets and urinals or treat 50% of wastewater on-site to tertiary standards.

  • Water Use Reduction, 30% - 40% reduction – 2-4 points (WE Credit 3)

Maximize water efficiency within building to reduce the burden on municipal water supply & wastewater systems. Use alternative on-site sources of water such as rainwater, stormwater and graywater for non-potable applications such as toilet flushing and urinal flushing.

  • Innovation Design Credit - 1 point (ID Credit 1-1.5)

Projects that result in exceptional performance above the requirement set by LEED.

EPA WaterSense

The EPA WaterSense partnership program discusses federal ratings standards for graywater. EPA WaterSense recognizes that the National Science Foundation (NSF) International has established a wastewater treatment task group for onsite residential and commercial graywater treatment systems. The NSF drafted a new standard, NSF 350 - Onsite Residential and Commercial Reuse Treatment Systems, which encompasses residential wastewater treatment systems along with systems that treat only the graywater portion. The EPA and CDC assembled experts to explore the science available for addressing high-priority regional needs such as graywater risk to humans and ecosystems and risk management options for graywater.[119]

Annotated Water Savings

Summary of Individual Studies Whitney et al. (1999) estimate the savings from a graywater system to be 446,200 gallons over a 15-year life span. The per capital annual average discharge to the landscape site was 20.4 gallons per day.

The California Department of Water Resources Graywater Guide (1994) estimates daily graywater flows for each occupant in a single-family residence. Graywater flow per day per occupant is the sum of flow from showers, bathtubs, washbasins, and clothes washers. Water savings is estimated as the amount of graywater flow that displaces landscape water use that would occur otherwise.

A direct method of estimating savings per household in a specific service area is to multiply graywater flow per person by the average number of persons per household in the agency service area. Presumably graywater displaces fresh irrigation water only for the part of the year that landscape is irrigated. Note that usable yield depends on gray water storage capacity and the irrigation requirements at the site, which under current health codes, can be met using graywater.

A study that considers the persistence of savings from household graywater systems has not yet been found.

Savings estimates are situation specific and need to account for slope of landscape, vegetation, climate, level of maintenance and other factors.

Confidence in Estimates
Medium-Low. Future efforts should include empirical measurement of water savings considering behavior (e.g., maintenance), the presence of other low flow devices (e.g., low flow showerheads, faucet aerators, and washing machines), and persistence of savings. Savings estimates may be confounded if wastewater were to be recycled (potential overestimate) or if water percolates to the groundwater basin rather than lost to the sewer (potential underestimate).

Related Literature

File:2.2 Graywater-CSS-2005.pdf

DWR (1994) California Department of Water Resources, "Using Graywater in Your Home Landscape: Graywater Guide," December.

Whitney et al. (1999) [A. Whitney, R. Bennett, C.A. Carvajal, and M. Prillwitz], “Monitoring Graywater Use: Three Case Studies in California,” (undated, assume 1999).


  1. City of Palo Alto, Water Conservation – Residential, California’s Water Conditions, (n.d.),
  2. Scholze, Richard. September 30, 2011, Public World Technical Bulletin 200-1-101: Graywater Applications for Army Installations,
  3. Scholze, Richard. September 30, 2011, Public World Technical Bulletin 200-1-101: Graywater Applications for Army Installations,
  4. Ibid.
  5. Art Ludwig, Oasis Design, 2009, Graywater to be legalized in California?,
  6. Scholze, Richard. September 30, 2011, Public Works Technical Bulletin 200-1-101: Graywater Applications for Army Installations,
  7. “Since 1 January 2008, appropriately treated greywater can be used for other purposes such as toilet flushing, laundry use (cold water source to washing machines), vehicle washing, path or wall washdown and lawn and garden spray irrigation.” Queensland Government. Department of Local Government and Planning, Greywater Use (n.d.),
  8. Art Ludwig, Oasis Design, What is Greywater, (n.d.)
  9. Department of Water Resources, CA Water Code, Section 145875-14877.3, (n.d.)
  10. Wholly H2O, Blackwater, (n.d.)
  11. Central Coast Graywater Alliance, Guidelines for Irrigating with Graywater (n.d.)
  12. Richard J. Scholze, September 30 2011, Graywater Application for Army Installations: Public Works Technical Bulletin: 200-1-101,
  13. Richard J. Scholze, September 30 2011, Graywater Application for Army Installations: Public Works Technical Bulletin: 200-1-101,
  14. Richard J. Scholze, September 30 2011, Graywater Application for Army Installations: Public Works Technical Bulletin: 200-1-101,
  15. Richard J. Scholze, September 30 2011, Graywater Application for Army Installations: Public Works Technical Bulletin: 200-1-101,
  16. Ibid.
  17. San Francisco Public Utility Commission, San Francisco Graywater Design Manual for Outdoor Irrigation,
  18. Art Ludwig, Oasis Design, Error: Storage of Grey Water, (n.d.); Bahman Sheik, 2010, WateReuse Foundation, White Paper on Graywater,; Marsha Duttle, 1990, New Mexico State University, Safe use of Household Graywater,; Richard J. Scholze, September 30 2011, Graywater Application for Army Installations: Public Works Technical Bulletin: 200-1-101,
  19. Richard J. Scholze, September 30 2011, Graywater Application for Army Installations: Public Works Technical Bulletin: 200-1-101,
  20. Art Ludwig, Oasis Design, Error: Storage of Grey Water (n.d.);
  21. San Francisco Public Utility Commission, San Francisco Graywater Design Manual for Outdoor Irrigation, (n.d.)
  22. Janet Nolasco, Pacific Institute, Sustainable Water Management for Urban Agriculture: Planting Justice, (n.d.),
  23. Art Ludwig, Oasis Design, Why use graywater?, (n.d.); Laura Allen, Wholly H2O, Uses and benefits of Graywater,(n.d.); Let’s Go Green, Practical Alternatives to Sewer and Septic System”, (n.d.); Eco-friendly Mind, Benefits of Gray Water Recycling,; Joe Gelt, University of Arizona, Home Use of Graywater, Rainwater Conserves Water--and May Save Money, (n.d.)
  24. Bahman Sheik, WateReuse Foundation, 2010, White Paper on Graywater,
  25. R. Penn, M. Schultze, E. Friedler, Grand Water Research Institute, February 2011, Effects of Greywater Use on Municipal Sewer Systems,
  26. Bahman Sheikh, WateReuse Foundation, 2010, White Paper on Graywater,
  27. Laura Allen, Greywater Action, Manufactured Greywater Systems, (n.d.)
  28. Art Ludwig, Common Grey Water Errors and Preferred Practices: An ongoing effort to counter the tidal wave of grey water misinformation on the web, (n.d.)
  29. Practically Green, Place Bucket in Shower and Use Gray Water for Plants and Garden, (n.d.); Sydney Water, Ways Greywater Can Be Used, (n.d.)
  30. Lane Cove Council, Manual Bucketing Guidelines, (n.d.)
  31. San Francisco Public Utility Commission, San Francisco Graywater Design Manual for Outdoor Irrigation, (n.d.)
  32. Laura Allen, Wholly H2O, Graywater Overview, (n.d.)
  33. Art Ludwig of Oasis Design originally designed the “Laundry to Landscape” systems. Oasis Design, Laundry to Landscape Grey Water System (also known as Laundry to Mulch Basins and Drumless Laundry Graywater System), (n.d.)
  34. Art Ludwig of Oasis Design originally designed the “Laundry to Landscape” systems. Oasis Design, Laundry to Landscape Grey Water System (also known as Laundry to Mulch Basins and Drumless Laundry Graywater System), (n.d.)
  35. Art Ludwig, Oasis Design, Laundry to Landscape Grey Water System, (n.d.)
  36. Alliance for Water Efficiency, Residential Clothes Washer Introduction, (n.d.)
  37. William B. DeOreo, Peter Mayer, Leslie Martien, Matthew Hayden, Andrew Funk, Michael Kramer-Duffield, and Renee Davis, Aquacraft, July 2011, California Single-Family Water Use Efficiency Study,
  38. William B. DeOreo, Peter Mayer, Leslie Martien, Matthew Hayden, Andrew Funk, Michael Kramer-Duffield, and Renee Davis, Aquacraft, July 2011, California Single-Family Water Use Efficiency Study,
  39. San Francisco Public Utility Commission, San Francisco Graywater Design Manual for Outdoor Irrigation, (n.d.)
  40. Ibid
  41. Laundry – 24%, Faucets – 16%, Bath – 2%, Showers – 18%
  42. San Francisco Public Utility Commission, San Francisco Graywater Design Manual for Outdoor Irrigation, (n.d.)]
  43. Art Ludwig, Oasis Design, Indoor Gray Water Reuse, Cascading, Gray Water Heat Recovery, and Rainwater Harvesting, (n.d.); Ecliissi Lifestyle,
  44. Wahaso Water Harvesting Solutions, Greywater Harvesting Systems From Water Harvesting Solutions, (n.d.)
  45. Laundry – 24%, Faucets – 16%, Bath – 2%, Showers – 18%
  46. San Francisco Public Utility Commission, San Francisco Graywater Design Manual for Outdoor Irrigation, (n.d.); Sonoma County Water Agency, Graywater, (n.d.)
  47. Chuck Ross, Lowe’s Commercial Services, Greywater Designs Offer Green Potential, (n.d.)
  48. Pete Melby, Tom Cathcart, 2002, Regenerative Design Techniques, Google On Line Books,; E. Erikssona, E. Donnerb, Technical University of Denmark, May 2008, Metals in Greywater: Sources, Presence and Removal Efficiencies,
  49. California Department of Housing and Community Development, 2010, California Plumbing Code, California Code of Regulations, Title 24, Part 5, Chapter 16A, Part 1 (GRAYWATER STANDARDS),
  50. Marsha Duttle, University of New Mexico, 1990, Safe Use of Greywater, Guide M-106,
  51. Chart includes water sources not currently legal in California – namely kitchen sink.
  52. Waterscape, Residential Sources of Contamination, (n.d.); Lentech, Sources of Groundwater Pollution, (n.d.); Wisconsin Groundwater Coordinating Council, 2002, Residential Development and Groundwater Resources,; University of Arizona, Pharmaceuticals In Our Water Supplies: Are “Drugged Waters: a Water Quality Threat?,; Miranda S. Fram, Kenneth Belitz, May 2011, Science of the Total Environment, Occurence and Concentration of Pharmaceutical Compounds in Groundwater used for Public Drinking-Water Supply in California,
  53. Marsha Duttle, New Mexico State University, 1990, Safe Use of Household Greywater Use, http//"
  54. Ibid
  55. San Francisco Public Utility Commission, San Francisco Graywater Design Manual for Outdoor Irrigation,; Oasis Design, Branched drain Greywater Systems,; Wholly H2O, Typical Graywater Components,; Greywater Action, Branched Drain Systems,
  56. Clean Water Components, Branched Drain Greywater System, (n.d.); John Russell, Watersprout, Greywater Systems: Branched Drains, (n.d.); Art Ludwig, Oasis Design, Builder’s Greywater Guide: Installation of Greywater Systems in New Construction and Remodeling, (n.d.)
  57. Laura Allen, Wholly H2O, Uses and Benefits of Graywater,
  58. Central Coast Graywater Alliance, Guidelines for Irrigating with Graywater, (n.d.)
  59. Lucy Allen, Juliet Christian-Smith, Meena Palaniappan, Pacific Institute, November 2010, Overview of Greywater Reuse: The Potential of Greywater Systems to Aid Sustainable Water Management,; Dayna Yocum, University of California, Santa Barbara, Design Manual: Greywater Biofiltration Constructed Wetlands Guide,;
  60. Lucy Allen, Juliet Christian-Smith, Meena Palaniappan, Pacific Institute, November 2010, Overview of Greywater Reuse: The Potential of Greywater Systems to Aid Sustainable Water” Management,; Richard Schloze, September 2011, Graywater Application for Army Installations,
  61. Greywater Action, Wetland Information, (n.d.)
  62. Dana Yocum, University of California at Santa Barbara, Design Manual: Greywater Biofiltration Constructed Wetland System,
  63. Dana Yocum, University of California at Santa Barbara, Design Manual: Greywater Biofiltration Constructed Wetland System, (n.d.); Lonny Grafman, Appropedia, Subsurface Flow Constructed Wetland for Greywater, (n.d.); A.W. Jokerst, L. A. Roesner, and S.E. Sharvelle, Colorado State University, An Evaluation of Graywater Reuse Utilizing a Constructed Wetland Treatment System,; Federal Ministry for Economic Cooperation and Development, Technology Review of Constructed Wetlands: Subsurface Flow Constructed Wetlands for Greywater and Domestic Wastewater Treatment,; A. Gross, O. Shmueli, Z. Ronen, E. Raveh, Recycled Vertical Flow Constructed Wetland (RVFCW) – A Novel Method of Recycling Greywater for Irrigation in Small Communities and Households, and Removal of Microorganisms from Domestic Greywater Using a Recycling Vertical Flow Constructed Wetland (RVFCW),; Graywater Action, Wetland Information,; San Luis Obispo, Guide to the Use of Graywater, (n.d.); Ronnie Frazer-Williams, Lisa Avery, Gideon Winward, Paul Jeffrey, Chris Shirley-Smith, Shuming Liu, Fayyaz Ali Memon, Bruce Jefferson, Cranfield University, Constructed Wetlands for Urban Grey Water Recycling,
  64. Brad Lancaster, Rainwater Harvesting for Drylands, Soap and Detergent Info, (n.d.) htttp://; Graywater Action, Frequently Asked Questions, (n.d.); Ecology Center, Guide to Greywater-Compatible Cleaning Products, (n.d.)
  65. California Department of Water Resources, January 1995, Graywater Guide: Using Graywater in Your Landscape,
  66. Greywater Action, Frequently Asked Questions, (n.d.); Ecology Center, Guide to Greywater-Compatible Cleaning Products, (n.d.)
  67. Alliance for Water Efficiency, Graywater Recovery and Treatment Systems, (n.d.)
  68. William B. DeOreo, Peter Mayer, Leslie Martien, Matthew Hayden, Andrew Funk, Michael Kramer-Duffield, and Renee Davis, Aquacraft, July 2011, California Single-Family Water Use Efficiency Study,
  69. Advanced Greywater Recycling Systems, Greywater Recycling, (n.d.)
  70. USEPA, 2011, EPA Water Recycling and Reuse: The Environmental Benefits
  71. The American Water Works Association Research Foundation (AWWARF), 1999, The Residential End Uses of Water study (REUWS).
  72. The American Water Works Association Research Foundation (AWWARF),1999, The Residential End Uses of Water study (REUWS), (n.d.)
  73. Joe Gelt, Water Resources Research Center, Home Use of Graywater, Rainwater Conserves Water – and May Save Money, (n.d.)
  74. Marsha Duttle, University of New Mexico, 1990, Safe Use of Greywater, Guide M-106,
  75. Bahman Sheik, 2010, WateReuse Foundation, White Paper on Graywater,
  76. Ibid
  77. Yorum Cohen, UCLA Institute of the Environment and Sustainability, 2009, Graywater- A Potential Source of Water,
  78. Yorum Cohen, UCLA Institute of the Environment and Sustainability, 2009, Graywater- A Potential Source of Water,
  79. Kreysig, D. Greywater recycling: treatment techniques and cost savings. Water Conservation Recycling 19(3):18–19. (1996)
  80. Alison Whitney, Richard Bennet, Carlos Arturo Carvajal, Marsha Prillwitz, Oasis Design, Monitoring Graywater Use, Three Case Studies in California, (n.d.)
  81. Bahman Sheik, 2010, WateReuse Foundation, White Paper on Graywater,
  82. Richard J. Scholze, September 30 2011, Graywater Application for Army Installations: Public Works Technical Bulletin: 200-1-101,
  83. Bahman Sheik, 2010, WateReuse Foundation, White Paper on Graywater,
  84. Greywater Action. Retrieved from
  85. Ibid.
  86. World Health Organization (WHO), 2006, Overview of graywater management: health considerations,
  87. Greywater Action, Health Studies of Greywater, (n.d.)
  88. Better Health Channel, Graywater-Recycling at Home, (n.d.)
  89. Australian Capital Territory, 2007, Guidelines for residential properties in Canberra,
  90. Oasis Design, Grey Water, (n.d.)
  91. Monash University, The University of Melbourne, 2011, Water Quality and Research Australia, Understanding Graywater use Around the Home-Report to Participants,
  92. South African Water Research Foundation, 2011, Safe Use of Graywater for Urban Food Production,
  93. Ottoson J., Stenstrom T.A. 2003, Faecal contamination of greywater and associated microbial risks. Water Research.
  94. Yorum Cohen, UCLA Institute of the Environment and Sustainability, 2009, Graywater- A Potential Source of Water,
  95. Australian Government’s National Rainwater and Greywater Initiative (NRGI) 2009,
  96. Ibid.
  97. Yorum Cohen, UCLA Institute of the Environment and Sustainability, 2009, Graywater- A Potential Source of Water,
  98. San Francisco Public Utility Commission, Graywater (n.d.)
  99. Soquel Creek Water District, Graywater Rebate. (n.d.)
  100. City of Santa Rosa, Graywater Rebate Program, (n.d.)
  101. East Bay Municipal Utility District (EBMUD), WaterSmart Rebate Program, (n.d.)
  102. State of Arizona, Arizona Graywater Conservation Tax Credit for Gray Water, (n.d.)
  103. Bahman Sheik, 2010, WateReuse Foundation, White Paper on Graywater,
  104. Yorum Cohen, UCLA Institute of the Environment and Sustainability, 2009, Graywater- A Potential Source of Water,
  105. Bahman Sheik, 2010, WateReuse Foundation, White Paper on Graywater,
  106. The Graywater Alliance, California Plumbing Code (Title 24, part 5, Chapter 16A, Part 1), (n.d.)
  107. OneCle, Texas Health & Safety Code - Section 341.039, 2012, Graywater Standards,
  108. Water Wise Group, 2012, Summary of Arizona Tax Credits,
  109. Government of Western Australia, 2010, Code of Practice for the Reuse of Greywater in Western Australia,
  110. New South Wales Government, Water for Life, Greywater, (n.d.)
  111. GreySmart. Rules and regulations state by state in Australia, (n.d.)
  112. Yorum Cohen, UCLA Institute of the Environment and Sustainability, 2009, Graywater- A Potential Source of Water,
  113. Wholly H2O, Graywater Codes and Regulations, (n.d.)
  114. Ibid.
  115. California Green Building Standards Code, California Code of Regulations Title 24, Part 11, 2010,
  116. U.S. Green Building Council, 2008, LEED for Homes Rating System,
  117. Ibid.
  118. Ibid.
  119. U.S. Environmental Protection Agency Municipal Support Division Office of Wastewater Management., 2004, Guidelines for Water Reuse,
Facts about "Graywater"
Has general subjectBenefits and costs +, Landscape + and Recycled and alternative water supplies +
Has introductionThe state of California and local jurisdictions can encourage safe and legal water reuse which allows the maximization of water’s utility on-site and encourages the treatment of used water prior to discharge. +
Has source URL + and +
Is publication typeReports and studies +