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Location California, USA

This page addresses two topics:

  1. Current California Greywater Regulations
  2. Backyard Greywater Design Calculator

General information[edit | edit source]

Greywater (also called graywater or grey water or gray water) is wastewater that has not come in contact with fecal material and is intended for reuse in irrigation. Greywater is a common method of water reuse with the benefit of reducing water consumption and preserving the water resource.

Greywater may not come in contact with fecal material due to contamination from pathogens. While greywater must not contain fecal material, it usually contains soaps, cleaning products, food particles and dyes, which may have nitrates, phosphates, bacteria, bleaches, solids (organic and not), and foam causing elements. Using water that contains these contaminants may cause degradation to the surrounding environment, by changing the pH, overloading nutrients, and increases oxygen demand.[1] Degradation to the environment from greywater may be reduced by the use of a wetland treatment system by reducing the contaminates through biological treatment and generating a healthier and more productive ecosystem.

California greywater defined[edit | edit source]

Greywater, defined by the California Health and Safety Code (Section 17922.12a) is "untreated wastewater that has not been contaminated by any toilet discharge, has not been affected by infectious, contaminated, or unhealthy bodily wastes, and does not present a threat from contamination by unhealthful processing, manufacturing, or operating wastes." The Code also specifies what household sources can provide grey water: bathtubs, showers, bathroom washbasins, clothes washing machines, and laundry tubs. Any wastewater coming from kitchen sinks or dishwashers cannot be classified as greywater in California.

The California Water Code (Section 14877) defines a greywater system as "a system and devices, attached to the plumbing system for the sanitary distribution or use of greywater." The California Plumbing Code, specifically Title 24 sets the regulatory standards for plumbing and installations of greywater systems.

The United States has some of the most stringent requirements, with California having the first greywater code in the nation[2]. California's code has up until 2009, been very restrictive and in most circumstances made it infeasible to install a permitted system. On August 4, 2009, California Plumbing Code adopted new regulations to help provide flexibility with water reuse systems.

For more information on California greywater law go to Oasis Designs webpage.

California design criteria[edit | edit source]

The criteria set by Chapter 16A[3]are given below, however it is important to check with local enforcement agencies for other local rules and regulations.

California greywater systems are separated into three categories, each with different permitting requirements:

  1. Single Fixture or Clothes Washer
    • No permit required
  2. Single System
    • Exceeds washer or single fixture system
    • Discharge capacity is 250 gallons per day or less
    • Construction permit required
  3. Complex System
    • Multi-family or multi-dwelling unit
    • Discharge capacity is greater than 250 gallons per day
    • Construction permit required

Requirements for construction permits:

  • Applies for Single System or Complex Systems
  • Identify groundwater level and soil type for absorption qualities
  • All components must be water tight
  • Must be inspected by the appropriate enforcement agency
  • Other local regulations and inspection requirements many apply (contact local enforcement agency)

All California greywater systems must meet the following requirements:

  • No connection to a potable water system
  • Designed based on location, discharge capacity, soil type and groundwater level
  • The area of discharge must be on the same plot as the source, unless lawfully exempt.
  • No construction until plan is approved by appropriate enforcement agency(except for clothes washer or single fixture system)
  • Dual discharge must be available to switch between greywater and sewer
  • No diaper wash water or possible contact with any fecal material
  • Greywater may not
    • be used for spray irrigation
    • be allowed to pond
    • runoff from desired discharge location
    • discharge to storm sewer
    • discharge to surface body of water
  • The discharge point must be covered by 2 in (51mm) material (mulch, rock, soil)
  • The greywater can not be used on root crops or edible parts of food crops

Summary California Plumbing Code Ch. 16A[edit | edit source]

Cities or counties have the ability to add stricter standards to that of California's and care must be taken to address all local standards as well as state standards. Only state standards are discussed here. The objectives of Chapter 16A are to[3]:

  • conserve water by facilitating greywater use,
  • reduce the number of non-compliant greywater systems,
  • provide guidance, and
  • provide an alternative that would relieve stress on private sewage disposal systems.

Chapter 16A establishes minimum requirements for the installation of greywater systems. Part I of the code covers all persons and occupancies regulated by the Department of Housing and Community Development (HCD). The purpose of the code is to provide guidance to users while adding more flexibility to the process. This chapter of the code contains provisions which allows for the installation of limited types of greywater systems to be installed without a construction permit. However the code does not eliminate the need for persons considering the installation of a greywater system from contacting local authorities to ensure they are informed and in compliance with local requirements or prohibitions. The Department of Water Resources (DWR) adopted Part II of Chapter 16A,[3] which covers general permitting, labeling, signage, inspection and testing of the recycling water system. The main purpose of Part II of Chapter 16 is to insure the greywater system is identified so the public and persons work on or around the system are informed on the contents of greywater pipes.

Chapter 16A, "Nonpotable Water Reuse Systems" was added as an emergency greywater regulation to the 2007 California Plumbing Code. The regulations were identified as "emergency" to eliminate the 18 month waiting period that would otherwise have been required. Chapter 16A was approved by the California Building Standards Commission (CBSC) on July 30, 2009. The emergency regulations were filed with the Secretary of State on August 4, 2009, effective immediately upon filing. The Nonpotable Water Reuse Systems (Chapter 16A) is now part of Title 24, under Part 5 of the 2007 California Plumbing Code and was made a permanent part of the HCD Plumbing Code on January 27, 2010, with the unanimous approval of the CBSC. Title 24, Part 5, Chapter 16A "Nonpotable Water Reuse Systems" (Parts I and II)

Subsurface greywater wetland design and calculator[edit | edit source]

Subsurface flow wetlands are the ideal choice for a greywater wetland that meets California regulations. A constructed wetland can be used in greywater applications for greywater treatment to help reduce pollutants before the water is released for irrigation.

Greywater is discharged from the house either directly into the greywater wetland or to a primary treatment system before going into the wetland.

Primary treatment[edit | edit source]

Primary treatment is needed if the effluent contains greases oils and large solids, as greases, oils and large solids can clog a wetlands and or kill beneficial bacteria, resulting in a reduction in the wetlands treatment function. Primary treatment separates out the larger solids greases and oils. Primary treatment can be accomplished with filters, grease traps and settling tanks.

After primary treatment the water undergoes secondary treatment in the greywater wetland through filtration and biological processes. The biological processes occur on the plants in the wetland via the bacteria that live on and around the vegetation and from decomposition of the fixed solids.

Primary treatment may not be necessary for California greywater systems, because kitchen sink effluent (the largest source of greases, fats and large particles) is not allowed in California greywater systems.

For more examples and ideas go to http://greywater.com/treatment.htm or Subsurface flow constructed wetland for greywater.

Greywater Subsurface Wetland Calculator[edit | edit source]

Snapshot of the greywater sizing calculator

An Excel Residential Subsurface Constructed Wetland Calculator has been designed to size a wetland for a household based on the biochemical oxygen demand (BOD) loading from a household[4][5]and California weather[6]. To download the calculator click here, the file must be saved and enabled before use.

To learn how to use the calculator click on the "How to Use the Calculator" link in blue located in the upper right corner of the Excel sheet or click on the "HowToUseCalculator" tab along the bottom.

Location[edit | edit source]

When selecting a location for a greywater wetland, consider the following:

  • The wetland should be directly on the receiving end of an effluent flow
  • A downhill slope of about 0.5% - 1%[4][5] is recommended so water can flow by gravity through the wetland and then to the final discharge area.
  • The site should be easily accessible for monitoring and maintenance.[5]
  • Do not construct the greywater treatment system in a pre-existing wetland.

Materials[edit | edit source]

Cut out of a subsurface wetland
Cut out of a subsurface wetland

Required materials for construction of a subsurface flow wetland.[4]

PVC or metal piping (inlet and outlet)
Fine plastic mesh
Impermeable linear
Check valve (back flow preventer)
Wetland Plants (Emergent plants for constructed wetlands)

Sizing[edit | edit source]

The design and sizing of a subsurface constructed wetland can be based on reduction of the biochemical oxygen demand (BOD). BOD is a water quality parameter that measures the amount of oxygen required for biochemical activity (e.g., aerobic bacteria) that is present in water to function. High levels of BOD in a system can decrease the available oxygen and be harmful to aquatic life.[7] The average BOD coming into the greywater wetland has been measured as 65 mg/L.[8] The final BOD in a natural system generally ranges from 2 to 7 mg/L.[4]

BOD removal rates can be calculated based on the reaction rate constant for the appropriate temperature using the equation below:[5]


kr = reaction rate for a specific temperature
k20 = reaction rate at 20 °C
T = lowest temperature in wetland system (°C)

The reaction rate constant varies bases on the system and the bacteria present. A larger k value indicates faster decomposition of BOD.[7] For the wetland design a k20 value of 1.1 day-1 was used for the reaction rate constant.[4] The area required for the desired BOD reduction can be calculated based on the detention time, which is a log order removal based on the reaction rate constant, and includes the flow, depth and the porosity of media


A = Area (m)
L = Length (m)
W = Width (m)
Q = Flow (m3/day)
Co = Initial concentration (mg/L)
Cc = Desired effluent concentration (mg/L)
d = Depth of gravel media (m)
n = Porosity of media (-)

Maintenance[edit | edit source]

Wetland treatment systems require limited maintenance, but some monitoring and initial work will provide better long term treatment. Several items of concernt are listed below:

  1. Water depth - To meet California requirements greywater is not allowed to pond up so maintain a wetland depth to insure all water is being treated below ground. During initial plant growth varying the water depth will encourage the roots of the plant to grow deeper providing more treatment at lower depths[4]
  2. Vegetation - Greywater should not be toxic to plants. Have your water tested if wetland plants are wilting and dying.[5]
  3. Invasive vegetation - the wetland vegetation should be monitored and maintained to ensure no invasive species are in the wetland as they may clog or reduce the wetlands treatment ability. In addition, if wetland plant species are not native, then vegetation from the wetland should not be allowed to migrate to any natural wetlands.
  4. Periodic cleaning - Primary treatment mesh screens will need periodic cleaning. The time between cleanings will depend on what the greywater system influent. The mesh screen be checked once a month for the first six month or until a cleaning schedule can be determined.
  5. Overflow from storms - heavy storm events will contribute water to the wetland. If there is a concern of the wetland over filling due to storm runoff, the the greywater system should be switched to a sewage system several days before the arrival of a storm of concern.

Resources[edit | edit source]

  1. Yocum, Dayna, 2006, Design Manual: Greywater Biofiltration Constructed Wetland System, Bren School of Environmental Science and Management, University of California, Santa Barbara
  2. Greywater Action, 2010, "About Greywater Reuse". <http://greywateraction.org/content/about-greywater-reuse>
  3. 3.0 3.1 3.2 HDC, 2010, "Nonpotable Water Reuse Systems", California Plumbing Code, Title 24, Part 5, Chapter 16A, Part I, <http://web.archive.org/web/20170218030139/http://www.hcd.ca.gov/codes/shl/Preface_ET_Emergency_Graywater.pdf>
  4. 4.0 4.1 4.2 4.3 4.4 4.5 Crites, Ronald, and Techobanoglous, Grorge, 1998, "Small and Decentrilized Wastewater Management Systems", Water Resources and Environmental Engineering
  5. 5.0 5.1 5.2 5.3 5.4 EPA, 1993, Subsurface Flow Constructed Wetlands for Wastwater Treatment: A Technology Assessment, Office of Water, 832-R-93-008
  6. Golden Gate Weather Services, 2011, <www.ggweather.com>
  7. 7.0 7.1 Metcalf and Eddy, 2003, Wastewater Engineering Treatment and Reuse, McGraw Hill, New York, NY
  8. Casanova, L.M., V.Little, R.J.Frye, and C.P.Gerba 2001. A survey of the microbial quality of recycled household graywater. Journal of the American Water Resources Association (JAWRA) 37(5)
FA info icon.svg Angle down icon.svg Page data
Keywords greywater, constructed wetlands, regulations
SDG SDG06 Clean water and sanitation
Authors Teresa Garrison
License CC-BY-SA-3.0
Language English (en)
Translations Russian
Related 1 subpages, 2 pages link here
Aliases California Greywater Regulations and Design
Impact 3,788 page views
Created November 16, 2011 by Teresa Garrison
Modified October 23, 2023 by Maintenance script
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