This article was originally published in the July/August 1995 issue of Home Energy Magazine. Some formatting inconsistencies may be evident in older archive content.
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Home Energy Magazine Online July/August 1995
The use of graywater--recycled household water from showers, sinks, and clotheswashers--increased in California during the mid 1970s and again in the late 1980s and early 1990s. The reasons? Some homeowners sought ways to save their valued landscapes in response to bans on outside watering caused by severe water shortages. Others sought ways to reduce their water use in response to skyrocketing drought-related water rates. Others were motivated by concern for the environment. Graywater use was approved, as a temporary drought measure, in both Marin and Santa Barbara Counties in California in 1978. The State of California even provided tax relief to individuals who installed graywater systems. A particular hotbed of graywater activity was found in several areas of Santa Barbara County. City of Santa Barbara officials, in response to a severe water shortage in 1990, requested a 45% cutback in residential water use and also a ban on outside watering. It was estimated that in the nearby city of Goleta 5,000 of 11,000 residents had some form of graywater system in 1989.
Graywater is generally defined as untreated used household water from showers, bathtubs, bathroom washbasins, and clotheswashers. Graywater from these household sources can be used in the landscape, provided that it meets certain conditions.
Wastewater from toilets and from soiled diapers is not approved because it may contain disease-carrying viruses or bacteria. Wastewater from kitchen sinks and dishwashers is not approved because it poses problems associated with grease, food particles, and detergent. Wastewater from water softeners is not recommended because it contains high concentrations of salt.
A graywater system in the 1970s was often no more than a garden hose going from the bathtub or washing machine out to the garden. Graywater systems gradually got more sophisticated in the late 1980s, as guidelines for the safe use of graywater were developed, largely in response to concerns on the part of public health officials. Graywater guidelines quickly led to the formulation and adoption of graywater standards in the early 1990s, which became part of both the Uniform Plumbing Code and the California Plumbing Code. Figure 1 shows a schematic of a graywater system. Today, 15 to 20 companies in California offer graywater systems ranging from do-it-yourself models to models that are fully automated and self-cleaning. While most graywater systems are found in California, they are appropriate wherever supplemental irrigation is normally required.
Although most homeowners who began using graywater did so to save their landscapes and reduce their water bills, many have discovered additional benefits. These include recovery of nutrients, reduced use of fertilizer, a healthier landscape, reduced septic tank flows, and various community benefits.
Household wastewater eligible for reuse in the landscape accounts for about 50% of indoor water use. For the average family of four this translates into a potential daily water savings of around 140 gallons or about 35 gallons per person per day. The actual annual water savings for each household depends upon indoor water use patterns, type of water using fixtures and appliances, the irrigated area, plant types, and the climate of the region.
A graywater system can be like a landscape insurance policy. If a water agency bans landscape irrigation during a severe water shortage, the graywater-irrigated landscape will survive. This can represent a significant cost avoidance to a homeowner, since the value of a landscape can often be 5%-10% of the value of a home. Using graywater also saves energy because when water travels from its source to house to sewage plant, energy is used to pump and treat it.
Using graywater improves the efficiency of applied water because it is delivered to the plants underground--eliminating runoff, overspray, and evaporation.
Valuable plant nutrients, such as phosphorous and potassium, are often found in graywater. Graywater use can result in healthier plants and in the reduced application of fertilizers. And, by leaving the soil surface drier, it may also make for a healthier landscape by reducing disease and pests.
Homeowners sometimes remove graywater streams from their household waste streams to reduce the flow to their septic tanks. This provides for longer treatment times and reduces the hydraulic loading on their leach lines.
The community benefits from graywater use because it reduces the amount of wastewater that is discharged to the local treatment facility. This has the potential to reduce wastewater treatment costs and may even postpone or avoid the need for flow-related expansions of the facility. Local water and wastewater agencies also experience reduced pumping costs.
A graywater system has three distinct elements: the drain-line plumbing, the surge tank and associated components, and the irrigation delivery system. Figure 2 (taken from Appendix J of the California Plumbing Code) identifies the various components of a graywater system where no pumping is required to deliver the graywater to the landscape.
Some plumbing work is required, however, because the graywater must be diverted from some of the existing drain lines. The various graywater source drain lines must then be connected to a common line to the surge tank which contains the valves, pumps, vents, controllers, and filters. Several types of these various components are available depending upon the level of sophistication desired. For example, the filter can range from a nylon stocking to a mesh screen to a sand filter.
Pumps are needed to deliver the graywater to the landscape if drip irrigation (rather than a leach field) is used or if the landscape is above the level of the surge tank. The size of the pump is determined by several factors. These are the height to which the graywater must be pumped (called head), the distance from the tank to the landscape, and the pressure required by the system to deliver the required discharge rate. For level lots, a 1/2-horsepower centripetal pump is usually adequate. For a family of four, the pump would run for about five minutes a day during the irrigation season and would draw 2 to 4 amps of power while running. While the homeowner would incur a slight increase in energy costs, the total energy use in the community would remain about constant since the water and wastewater systems would realize an energy savings due to reduced pumping costs.
One of the toughest challenges in designing the graywater system is laying out the irrigation system and determining the size of the area to be irrigated. The homeowner or designer must decide which plants can be irrigated with graywater. The irrigated area is determined by the type of soil, by the volume of graywater produced, and by the summer water requirements of the plants. Table 1 presents a hypothetical example for determining the water requirements of different plants.
Installation costs for graywater systems can range from several hundred dollars to more than $5,000. Table 2 compares the costs of installing various graywater systems. Note, however, that a fully automated, do-it-yourself system (except for the drain line plumbing and the irrigation system) recently became available for under $1,000. Table 3 itemizes the cost (based on 1994 figures) for each component of the graywater system.
Costs also depend on whether the system is going into an existing or new dwelling and whether the dwelling has a raised or slab foundation. Costs are usually lowest for new construction and highest for existing dwellings with slab foundations. In fact, it is so expensive to install a complete graywater system in an existing home with a slab foundation that only effluent from the washing machine should be considered in this situation.
Health and Water Quality
Two areas of concern regarding graywater use involve health and water quality. Since graywater can contain infectious organisms, safety standards were needed before health officials would sanction its use.
In 1991, the City of Los Angeles conducted a one-year study of graywater use at eight residential test sites to make recommendations for, among other things, the safe use of graywater. Bacteria in the soil were found at both graywater and nongraywater irrigated areas in the test landscapes. While bacteria increased in the soil where graywater was used, disease organisms were not found at any of the test sites. One conclusion was that graywater ... does not pose a significant risk to users or the community. Another finding of this study was that soils contain a lot of animal fecal matter. The results led one observer to conclude, Don't eat dirt. Note that although graywater has been used in California for about 20 years without permits, there has not been one documented case of disease transmission.
In 1992, Appendix G (originally Appendix W) was added to the Uniform Plumbing Code of the International Association of Plumbing and Mechanical Officials (IAPMO). This appendix established standards for the use of graywater in 22 Western states. In November, 1994, Appendix J of the California Plumbing Code went into effect, permitting the use of graywater in single-family residences for subsurface landscape irrigation. To date, California is the only state to adopt Appendix G, in a slightly modified form.
There are several important rules regarding the safe use of graywater. In California, graywater use is permitted only at single-family dwellings. The California Plumbing Code requires that graywater be delivered to the landscape through a mini-leach field (at least 17 in below the surface) or a subsurface drip irrigation system (at least 9 in below the surface) to avoid runoff, surface pooling, and spray (see Figure 3). The Uniform Plumbing Code does not permit the use of drip irrigation, only mini-leach fields, which must be 18 in below the surface. Graywater use is not permitted where soil conditions do not allow for adequate drainage or where groundwater could be contaminated (within 5 ft of the surface).
Some observers believe the codes could be improved if the subsurface application were allowed to occur within several inches of the soil surface to better irrigate those plants with shallow root systems and to take advantage of the higher concentration of bacteria in the soil. (Ninety percent of the bacteria in the soil occurs within the top 18 in.) Bacteria are responsible for the rapid breakdown of graywater constituents into water-soluble plant nutrients.
Cleansers to Avoid
While most detergents can be used with graywater systems, there are several important exceptions and several cautions. Products that contain boron, such as Boraxo and Borateam, should not be used. Boron has been shown to be very toxic to most plants. If salt buildup in the landscape is a concern (it should be, in most cases) it is better to use liquid detergents than powdered detergents. Powdered detergents contain excessive amounts of sodium, which is often used as a filler. Since detergents are alkaline, acid-loving plants (generally those which like shade, but check with the local nursery) should not be considered for graywater application. Homeowners with graywater systems generally need to be conscious of what they put into the graywater drain lines, from the type of laundry detergent to household cleaners.
Finally, graywater should not come in contact with the edible portion of fruits and vegetables (for instance, with root vegetables, such as carrots, radishes, potatoes, and beets).
Even in some areas affected by severe water shortages, graywater use is still quite low. A survey conducted in the East San Francisco Bay area in 1994 indicated that only 2% of single-family households had graywater systems and that about 25% of the people surveyed had never heard of the term graywater.
Bay Area water agencies requested up to a 25% cutback in water use during the 1987-1992 drought period. In areas where water agencies requested higher cutbacks and/or issued bans on outside watering, a higher percentage of graywater systems are found. Studies planned over the next few years will seek to determine
How people feel about their graywater systems.
Answers to these questions will shed more light on the real benefits and costs of using graywater.
Legislation recently introduced in California (Assembly Bill 313) would allow for the safe use of graywater at sites besides single-family residences. In the future, new single-family homes may even be required to be plumbed to allow for graywater use. Graywater use is expected to increase slowly as more people become aware of its benefits and as the costs of ensuring a reliable water supply increase.
Using Graywater in Your Home Landscape: Graywater Guide, California Department of Water Resources. P.O. Box 942836, Sacramento, CA 94236-0001.
Create an Oasis with Greywater: Your Complete Guide to Managing Greywater in the Landscape ($9) and Building Professionals Supplement: Your Complete Guide to Professional Installation of Graywater Systems ($13). Both available from Oasis Biocompatible Products, 5 San Marcos Trout Club, Santa Barbara, CA 93105-9726.
Dick Bennett is Water Conservation Administrator at the East Bay Municipal Utility District in Oakland, California.
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