Graywater For Gardens
During the 1977 to 1979 drought in California, desperate gardeners used water from washing machines, showers, bathtubs, kitchen sinks and dishwashers to sustain thirsty gardens. The East Bay Municipal Utility District in San Francisco even circulated a pamphlet detailing how to use this "graywater." But techniques and methods that were common in 1977 now appear ill-advised. The details for legal graywater use are drastically different from those unsanctioned systems of the late '70's. I should know -- back then I was hard at work installing what I now call "guerilla systems" in Marin County. Public health officials were aghast.
Succeeding droughts inspired research, conferences and, ultimately, legislation. Now graywater use is a legal option throughout California and in 22 western states. If you're building or remodeling, you can install a system with the confidence that it meets health and safety codes. If your graywater system works fine but is old and not up to new codes, you may be able to upgrade to modern guidelines.
Use of graywater on landscapes became legal in California in November 1994 with the adoption of Appendix J to the California Plumbing Code. The only exceptions are the cities or counties that specifically restrict or forbid graywater use with a local ordinance adapted prior to November 8, 1994.
A more timid ordinance, Appendix W of the Uniform Plumbing Code, was approved by the International Association of Plumbing & Mechanical Operators (IAPMO) on January 1, 1993. It applies to the 22 western states.
Refer to either of these two regulations when installing a graywater system, either in new construction or when remodeling. Your county planning or building department can provide Appendix W, and in California, Appendix J. Or write to the California Water Conservation Office (Department of Water Resources, Box 942836, Sacramento, CA 94236-0001) and ask for their booklet, Graywater Guide: Using Graywater in Your Home Landscape.
Graywater and Public Health
The bottom line is this: Don't use graywater on or near annual vegetables, annual ornamental bedding plants, or for any planting that requires working the soil several times per season. Use graywater around perennials, trees and shrubs only, and wash your hands after working in soil irrigated by graywater.
You can use graywater from your shower, bathtub, bathroom sink and laundry. Only these sources are included in the legal definition of graywater. Used water from kitchen sinks and dishwashers is excluded, less because of any potential health risk than because too much soap, oils, fats, particulates and food pieces clog pipes. Nevertheless, graywater is classified as "sewage waste." From a Public Health Department perspective, it is potentially as dangerous as the "blackwater" from a toilet. Graywater can contain the same pollutants and pathogens as blackwater, but usually in much smaller amounts.
The list of diseases potentially transmitted via graywater ranges from food poisoning to typhoid fever. Not one graywater-caused illness has been documented by any public health agency, however.
Keep Graywater Underground
The current approach emphasizes no "daylighting," or surface puddling. If the graywater-irrigated soil doesn't get moist on the surface, then nobody can come in contact with pathogens or parasites it may contain. Thus, in a modern graywater system, the graywater goes directly to the roots of trees and shrubs via subsurface distribution, either a shallow leachfield or buried drip irrigation.
A leachfield system utilizes a perforated pipe set 18 inches deep, surrounded by a trench of gravel and covered with nine inches of soil. Each perforated pipe should be set level and be no longer than 10 feet. (By comparison, a septic leachfield is four to six feet deep.) Best suited to watering trees and shrubs, this system features three main benefits: It's simple to operate, doesn't clog and works well if downhill from a gravity-feed system. Limitations include the difficulty of installation among existing plants, relatively inefficient use of water, uneven distribution and unsuitability for upward slopes.
Drip systems have several advantages. They apply graywater close to the soil surface for more aerobic "digestion" of its organic matter and nutrients. They spread the graywater over a large area, and deliver it to the largest number of plants with the greatest amount of control. Finally, a drip system is best if you're designing a system around slopes and grade changes, or simply dealing with heavy clay soil that's slow to accept water.
California's Appendix J requires that the in-line-emitter tubing (black plastic tubing with emitters installed inside the tubing at regular intervals, with an emitter flow of no more than 1/2 gallon per hour) be buried nine inches below the surface to prevent daylighting. The best tubing is made by Geoflow and is called Rootguard Emitter Line. A mail-order source is The Urban Farmer Store, 2833 Vicente St., San Francisco, CA; (800) 753-3747. A 100-foot roll costs $51.
The chief limitations of graywater distribution by drip are that the systems are more costly and complex, and inadequate filtration is a disaster. The lint, dirt and oils in graywater act like large logs, huge boulders and oil slicks in tiny in-line-emitter openings. Some systems filter the graywater with a fine-meshed bag, some with self-cleaning canisters of clean sand and others with paper-cartridge chambers. Most require diligent and frequent cleaning of the filter medium. A failed filter can permanently ruin the entire drip system in a very short period of time. And drip is not well suited to most gravity-feed graywater systems because they need some water pressure, at least 10 pounds per square inch (psi) of water pressure, the equivalent of a 23-foot drop in elevation.