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Greywater Basics

Greywater is a unique source of relatively clean residential wastewater that is used differently from potable (drinking) water and rainwater. Household sources of greywater include bathtubs, showers, bathroom washbasins, clothes washing machines and laundry tubs.

When Is a Permit Required?

A construction permit is NOT required for a greywater clothes washer system in compliance with the California Residential Greywater Code (California Plumbing Code, California Code of Regulations Title 24, Part 5, Chapter 16). Below is some information on greywater clothes washer systems.

  • A “greywater clothes washer system” is defined as a system utilizing only a single domestic clothes washing machine in a one- or two-family dwelling.
  • The method for converting it cannot use a secondary pump and must utilize the machine’s pump, or a gravity pump to irrigate garden areas.
  • The amount of water from the washing machine is approximately 15 gallons per wash.
  • Laundry soaps used must be biodegradable and non-toxic. They should also be free of salt (sodium) and boron (Borax) two common ingredients that are non-toxic to people, but harmful to plants and soil. Hydrogen peroxide bleaches should be used instead of chlorine bleaches. 

Permits are required for all other greywater construction efforts. For example, you will need a permit for a greywater system for outdoor irrigation if the system meets any of these conditions:

  • Collects water from showers, sinks, or baths;
  • Alters the plumbing (i.e., whenever you cut into the drainage plumbing to access the greywater);
  • Is installed in a building that is not a one- or two-unit residential unit; and/or
  • Includes a pump (besides the washing machine’s internal pump) or a tank.

For additional information about plumbing and permitting a greywater system, contact the Building Division at (805) 449-2500 or click onto their webpage.

Greywater Resources

Relevant Greywater Codes

Chapter 16A: Establishes the minimum requirements for the installation of greywater systems in housing units regulated by the Department of Housing and Community Development (HCD). It is intended to provide code with enough flexibility to encourage the use of greywater.

For a laundry greywater system, it is suggested that all systems have a courtesy review by our Building Division during the design phase to prevent any plumbing or siting issues or environmental risks.


The new laws requiring “California to Make Water Conservation a Way of Life” will establish an allowance for the amount of water used per person and the amount allocated for outside irrigation. It will be a few years before the rules take effect, but residents are encouraged to start planning for these changes by taking advantage of rebate programs to buy energy efficient appliances, remove turf or install rainwater capture devices.  One option to capture rainwater is a cistern which can be used as part of a rainwater collection system and is eligible for a rebate.

Cisterns are large tanks or containers that store water collected from rainfall. Collecting and reusing rainwater can be a great way to conserve resources. For reference, one inch of rain falling on a 1,000 square-foot roof can produce 623 gallons of water. This is a significant amount for irrigation use.

Cisterns are an excellent alternative for those looking to take advantage of the wet season, and they are eligible for up to $350 in rebates from They can help residents to conserve additional water, reduce stormwater runoff and the amount of water taken from California’s reservoirs. For more information on cisterns and their use, please visit the County of Ventura’s article on rainwater cisterns (PDF).

For those interested in installing cisterns on their property, the City of Thousand Oaks’ building codes allows their construction without permits under certain conditions:

  • Any free-standing outdoor water tanks must not exceed 5,000 gallons.
  • The height to width ratio must not exceed 2 to 1 (i.e., a 3-foot wide tank can be no more than 6 feet tall).
  • Cisterns must not be visibly obtrusive to other residents. If it is visible, a covering or screen may be required. Please check with the Planning Department for details.
  • Although not required, the City recommends that residents check with the Planning and Building Divisions of the Community Development Department before starting any installment projects. Depending on the project, additional building permits might be required.
  • Additional recommendations residents should be aware of before installing a cistern include:
    • Make sure that any placement is stable and strong enough to support the cistern (water weighs about 8 pounds per gallon).
    • Be aware of the chance for your tank to overflow. Rainstorms can produce more than six inches of rain per day.
    • Regularly maintain your roof and gutters. If not screened or cleaned regularly, debris can get washed into the tank. (Installing a self-cleaning screen or filter at the inlet of the tank can help avoid this).
    • Standing water is an ideal home for mosquitoes. Potential solutions include: having a tight-fitting lid to prevent mosquitoes from entering; installing a screen over any openings; adding anti-mosquito larvae chemicals; and dumping the collected water every two weeks, or earlier.
    • Understand the health risks involved with using water from cisterns. Rainwater can contain, or pick up harmful chemicals and pathogens that can make you ill and should only be used for outside irrigation. For more information on preventing illness from rainwater collection systems, please check the CDC’s webpage.

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