What is Graywater?
Graywater is wastewater from laundry machines, bathroom sinks, showers and bathtubs but not from kitchen sinks, dishwashers, toilets or waste from dirty diapers. Appropriate reuse of graywater facilitates water conservation, relieves stress on septic systems and can be done safely and effectively if we follow the guidelines preventing potential health threats and environmental contamination.
California Plumbing Code
To begin, familiarize yourself with the California Plumbing Code. The CPC provides important information regarding how to build a graywater system avoiding surfacing or runoff, groundwater contamination and human or pet contact with wastewater.
To build a graywater system that is connected to a shower, tub or sink, a Building Permit is required. For guidelines on how to obtain a permit please see the Planning Department Website.
Laundry to Landscape Systems
Laundry to Landscape system is the only graywater system exempt from a permit. For guidelines on how to build a laundry to landscape system refer to: Laundry to Landscape Graywater System Design Guidelines. You can also watch a video about the process by clicking here.
For information on professional graywater irrigation contractors in Santa Cruz County visit the Central Coast Graywater Alliance website.
Designing the system
To design a system, start by evaluating the slope and soil type of the proposed irrigation area. CPC Table 16A-3 lists the various types of soil and how much graywater should be discharged per day based on percolation rate. Parcels with a slope of 30% or greater are considered inappropriate for graywater irrigation. Santa Cruz County GIS layer can help determine if your soil type and slope are appropriate. To avoid contaminating ground water, dig a 3 1/2 ft. hole in your yard to determine if you have high ground water. If ground water is seeping into the hole, the property may not be appropriate for a graywater system. All systems are required to have a shut off valve, which is easily accessible and diverts graywater to the building sewer. All graywater systems should be shut off during the winter rainy season, as plants will not need extra water and there is an increased chance of runoff and contamination of creeks, rivers and ground water. Sizing the system correctly is extremely important, as the irrigation area should be able to accept all the water that will be discharged without having any overflow surfacing or running off. It is equally important that the system provides enough water to the irrigation zones that your plants aren't under watered either. Assuming there is not high ground water, the system needs to be sized according to the type of soil and its percolation rate. Table 16A-2 will give you a specific square footage of irrigation area per 100 gallons of graywater to be discharged. You may calculate your estimated graywater use based on winter water use records, calculations of local daily per person interior water use. Or estimate your graywater usage using the procedure in the CPC.
Soap and Detergents
To keep your plants healthy it is best to avoid soaps which contain chlorine or bleach, salts such as sodium or sodium combinations peroxygen, sodium perborate, sodium trypochlorite, boron, borax, petroleum distillate, alkylbenzene, “whiteners,” “softeners” and “enzymatic” components. Click here for more information.
For more information on graywater contact:
Santa Cruz County Environmental Health Services