Measurement & Modeling of Quality Changes in Untreated Grey Water

Graywater is used household water that is recycled immediately outside the house, generally to flush toilets and water non-edible landscapes. Graywater is shower, sink and wash water that contains no sewage solids and no non-biodegradable soaps, detergents or cleaners. Because the use of graywater still raises some environmental and public health concerns, monitoring graywater quality to determine the most effective systems is important.

Arizona's Models

• Arizona is a state with low annual rainfall and several centers of very high consumption. Water conservation is a big priority for the state. In response, the University of Arizona is working with two model residences, named Casa de Agua and Desert House, in Tucson and Phoenix respectively. Casa de Agua was retrofitted with water conservation systems, including a graywater system; and Desert House was designed and constructed with an integral original graywater system. Both systems have successfully treated graywater to meet with environmental impact standards, but the Casa de Agua system has proven prohibitively expensive for regular residential use. The College of Agriculture and Life Sciences has records for public review.

California

• In 1999, the California Department of Water Resources conducted a study of graywater systems in conjunction with three cities: Santa Barbara, Oakland and Sacramento. Testing was done by taking soil cores at every depth around irrigation outlets to six inches below the subsoil. Samples were tested for both pathogens and chemicals. Samples were also taken from surge-tanks and settling tanks, but researchers agreed that the soil samples were the most valuable measurements. Conclusions were that chemicals were the greatest concern and that the choice of cleaning products for the home were the most important variable.

Oregon

• In November 2010, the Oregon Department of Environmental Quality (DEQ) published its graywater guidelines that corresponded to House Bill 2080 allowing graywater permits to be issued to residents of the state. Included in those guidelines is a summary report on testing of various commercial graywater systems. Exit water was tested for each system to determine pH, a list of chemicals of concern and fecal coliform bacteria. These results are published in the DEQ publication entitled "Recommendations of Graywater Treatment, Disposal and Re-Use."

Colorado

• Colorado State University published the "Graywater Reuse and Rainwater Harvesting" fact sheet in 2009, wherein the emphasized the differences, and therefore differences in monitoring strategies required, between graywater systems. Graywater that strictly emanates from showers and bathroom sinks does not present the same potential problem as either kitchen sinks with grease and other nutrient solids, not the hazards associated with some laundry detergents and other laundry additives. Graywater that is being recycled strictly to flush toilets is mixing the second-use water with the normal sewage output, where it will be treated in existing sewage systems.