Graywater Irrigation as a Means to Meet Water Demands in Arid Regions

Graywater irrigation systems offer many benefits, however the use of such systems has not become widespread due to concerns about safety issues. While some states have begun to legalize and regulate the practice of graywater reuse for residential landscape, little guidance based on scientific data has been provided for the safe operation of graywater irrigation systems. Limited scientific data is available on the fate of graywater chemical and microbiological constituents and the effect of these constituents on plant health after graywater is applied for irrigation. In this research we have examined the long-term effects of graywater irrigation. We selected three households where graywater has been applied for irrigation for more than five years to include in this study located in California, Colorado, and Texas. Sampling locations were selected to encompass a variety of soil types and climatic conditions. Soil and plant samples have been collected in an area irrigated with graywater as well as a control area with analogous soil and landscaping that has been irrigated with potable water. Soil cores have been taken to a depth of 1 m and we have analyzed the presence of antimicrobials, and indicator organisms at depths of 0 – 13 cm, 13 – 30 cm, and 30 – 100 cm separately. Soil samples also were analyzed for indictor organisms including total coliforms, E. coli, Enterococci, Clostridium perfringens. In addition, infiltration tests were conducted in each sites to evaluate the effect of graywater on infiltration rate of soil.