Evaluation of Combined Rainwater and Greywater Systems for Multiple Development Types in Mediterranean climates

Jeff Loux, Rebecca Winer-Skonovd, Erik Gellerman



This paper explores the feasibility of combining rainwater harvest and greywater capture to meet urban water demands such as toilet flushing and landscape irrigation. In Mediterranean climates, rainwater harvesting is not a viable year-round alternative water supply. On the other hand, greywater has issues of quality, storage and plumbing costs. Three land uses (single-family house, apartment cluster, and mixed use site) were analyzed to determine the viability of rainwater and greywater in combination as a realistic water supply for non-potable uses. In all three development scenarios, rainwater and greywater combined were capable of offering sufficient volume of water to meet irrigation and toilet flushing demands. Several major impediments exist to the widespread adoption and use of combined rainwater and greywater systems the largest of which may be cost. An analysis of cost revealed that onsite use of rainwater/greywater in the single-family house scenario is nearly three times more than a municipal (City of Davis, CA) water bill. The discrepancies in cost do begin to level out at higher densities. Rainwater and greywater harvesting will be most successful if it is considered in the early planning stages. Additional areas for further investigation are suggested.


Keywords: Greywater; Rainwater harvesting; Reuse; Stormwater; Water conservation; Water management