Frequently Asked Questions about Graywater

Graywater is untreated wastewater that has not been contaminated by any toilet discharge. Graywater includes wastewater from bathtubs, showers, bathroom sinks, clothes washing machines and laundry sinks. It does not include wastewater from kitchen sinks, dishwashers, photo lab sinks or laundry water from soiled diapers.

Graywater systems are onsite wastewater systems that use graywater for subsurface landscape irrigation through the use of mulch basins, disposal trenches or subsurface drip irrigation fields.

The regulations for the design, construction and use of graywater systems can be found in Chapter 16 of the California Plumbing Code (CPC). A copy of these regulations can be found in the Well and Septic Systems area of this website.

Permit Sonoma (PRMD) has been delegated the authority to regulate graywater systems in the unincorporated area of Sonoma County by the California Regional Water Quality Control Board (RWQCB). Permit Sonoma does not regulate graywater systems in the incorporated cities in Sonoma County. These cities can implement a program of their own that meets or exceeds the requirements of the CPC with approval from the RWQCB. Questions regarding graywater systems within an incorporated city should go directly to that city.

Due to the potential for high levels of bacteria and viruses in graywater, graywater must be used in a way that eliminates potential human contact or the creation of nuisances. The regulations for graywater systems allows for subsurface irrigation only, although graywater can be discharged to the ground surface in a mulch basin as long as it remains covered with at least two inches of mulch, rock or soil.

The CPC allows graywater to be used for flushing toilets but the graywater must meet the same regulations in place for the use of recycled water (Title 22) with respect to treatment, permitting, inspection and cross connection control.

The CPC exempts graywater systems that collect graywater from a clothes washer only and where no modifications to the plumbing system are required or pumps are used in the graywater system from construction permits but the system must still meet the design and construction standards found in the regulations. All other graywater systems require a construction permit. Plans for graywater systems must be submitted to Permit Sonoma or the authorized permitting agency for review and approval of the graywater design. Once the design is approved, a construction permit must be obtained to install the graywater system and allow for inspection by the permitting agency.

You need to contact your local building department to discuss plumbing, venting and electrical requirements as needed for either new construction or the retrofit of an existing structure where a graywater system is proposed. In addition, you need to contact your local water purveyor to discuss the need for the installation of a backflow protection device at the water meter.

Graywater can be used to irrigate fruit trees, ornamental trees, shrubs, groundcover and lawns. Graywater should not be used in vegetable gardens where the food is a root crop or touches the ground surface. Be aware that soaps and detergents can contain a variety of chemicals to aid in cleaning that may be harmful to your plants. Please contact your local landscape specialist for more information.

Additional information regarding graywater and onsite wastewater systems is available on the Well & Septic pages. Permit Sonoma is currently in the process of developing new guidelines for the use of graywater to address the revisions to the CPC and will post these when available.