Residential Greywater System Study

We have completed the report on the results of our study on residential greywater systems in Central California. (Download links below.)

We studied 83 systems in the San Francisco Bay area, Monterrey Bay area, and the Santa Rosa area. We conducted interviews, collected and tested greywater and soil samples (analyzed at a laboratory), visually examined 127 plants irrigated with greywater, and conducted a separate survey of 20 professional greywater installers about installation costs for 259 systems they had collectively installed since 2009.


Overall, the greywater systems in our study saved water and had few problems.

Our key findings include:

  • Per capita water consumption decreased by an average of 17 gallons per day after greywater system installation. This translates to an average household savings of 14,565 gallons a year.
  • Greywater did not negatively affect either soil or plant health.
  • The quality of greywater was typically suitable for long-term irrigation of plants, so long as the household used products without sodium or boron compounds.
  • Most (99%) of system users were satisfied with their systems.
  • Though people did very little maintenance on their systems, no major problems developed. However, more education and a few changes in design can improve performance of greywater systems and avoid potential problems.

watersavings-monthDownload the executive summary, the report, and the appendices below.

Please direct comments, questions and suggestions to Laura Allen (