Desert Botanical Garden: THE DESERT HOUSE: Graywater

Saving money is on the minds of most Americans today, and recycling certain materials, i.e., aluminum cans, newsprint and plastic containers come to mind when the subject of recycling comes up. But what about recycling household water? In non-agricultural areas, household water use constitutes the largest share of water demand by communities throughout the United States. The Desert House incorporated two water recycling systems, graywater and rainwater.

Graywater recycling systems irrigate landscape plants and save money on water bills at the same time. At Desert House in 1996, over 11,000 gallons of water, out of a total of 104,000 gallons used on the landscape were recycled graywater. Graywater is waste water from showers, baths, bathroom sinks and washing machines. Blackwater is waste water from the toilet, dishwasher and kitchen sink, and must be directed to the sewer, the practice today, and it is never included with the graywater because of the possibility of spreading infectious disease. Close attention to the health of household members is important when using a graywater system. When a communicable disease, for example, hepatitis, flu, measles, etc., is diagnosed, graywater irrigation should be discontinued by diverting it into the sewer until the affected person has completely recovered. The Desert House graywater system diverts water from the shower/bathtub, bathroom sinks, and washing machine to two 4,700 gallon storage tanks located in the basement. Each tank has an overflow valve leading to the sewer to prevent overflow and flooding. A sand filter, much like a swimming pool filter, is used to remove unwanted solid material and a pump transports the graywater to the drip irrigation system located outside. Sensors measure the amount of graywater collected and stored so that future irrigation needs can be determined.

Installing a graywater system in a house under construction affords an economical opportunity to place the necessary plumbing to recover all graywater produced by the household. Retrofitting existing homes where the plumbing is located under a concrete floor is more difficult and expensive, and is usually limited to recovering washing machine water. In all cases valves must be installed so that graywater can be shunted to the sewer system when necessary. All materials necessary to construct a graywater system are available in building supply or plumbing stores.

Keeping track of what goes into the graywater system is very important. Detergents that include bleaches, softeners, enzymatic cleaning agents, and high salt concentrations must not be used. Chlorine bleaches, dyes and fabric softening agents are also to be avoided. Previous graywater research has demonstrated when the use of these products are necessary, graywater must be shunted to the sewer system to protect plants.

Graywater is suitable for many landscape plants, but the long term effects on many plants is unknown and there is some concern on the part of government public health agencies about the safety of graywater. As of 1997, the State of Arizona, unlike many states, has no legal mechanism or system of codes to approve and license graywater systems. The Desert Botanical Garden is hoping to help answer these questions with an experiment on the effects of graywater on ornamental plants. Portions of the Desert House plantings are watered with graywater while other portions are watered with city water. Results form this experiment are expected in 1999, and will be publicly available.