A final report detailing the state-of-knowledge regarding reusing household graywater in the landscape.
The use of household graywater for landscape irrigation is gaining in popularity in the United States. This literature review identifies the current state of knowledge regarding the long-term impacts of landscape irrigation with household graywater and identifies the knowledge gaps that need to be addressed in an experimental plan. The review examines overall graywater issues including: 1) quantity, quality, treatment methods, and legality; 2) potential effects of graywater on residential landscape plants; 3) potential effects of graywater on soil microbial function; 4) use of indicator organisms for human health considerations; and 5) soil chemistry changes due to graywater application.
Knowledge gaps were found in the following areas: 1) documentation on whether or not constituents in graywater will accumulate in the soil in sufficient quantities to harm plants or perhaps be transported below the root zone to the groundwater during the rainy season; 2) information on the effects of graywater irrigation on landscape plants, which are typically inferred from experiments with recycled treated wastewater used for irrigation; 3) information on both short-term and long-term effects of graywater irrigation on indigenous soil microorganism communities and their important ecosystem functions; 4) information on whether the indicator organism counts are an accurate predictor of an actual health threat posed to individuals coming into direct contact with graywater; and 5) guidance to help the homeowner design a proper graywater capture, storage and distribution system. A targeted research program is needed to address these knowledge gaps and it should include all applicable scientific disciplines. (2006) Water Environment Federation.