A backhoe lowers one of two 1,700 gallon cisterns into the ground. Photo: Diane Gleason
California will continue to have dry years and wet years and multi-year droughts. Most residents rely on massive state or federal systems for most of their water. But it would help everyone if residents relied more on local systems. Really local, as on your own property. Local water storage has advantages similar to putting solar panels on your roof: reduced dependency on distant sources.
A typical Santa Clara valley resident uses 100 gallons per day. The average household, with 2.3 people, uses 6,900 gallons per month, half of it outdoors. Summertime outdoor use can be five to ten times higher, so thousands of gallons need to be captured and stored to make a serious dent in residential outdoor water use. This is a serious challenge. To reduce outside water use, the most important changes are to get rid of the lawn and use efficient irrigation systems. For more on this, see the article below and the "Gardening Green" column on page 8. In addition to these improvements, you can build your own on-site water storage system.
Fortunately, all homeowners have the beginning of a home water storage system because they all have roofs. When one inch of rain falls on a 2,400 square foot roof, about 1,500 gallons runs off. The challenge is how to store it.
Some residents install rain barrels, which are an easy way to use rain runoff. Most rain barrels hold 50 gallons and cost between $50 and $350. However, 50 gallons is only enough to water a small garden once or twice. Even 10 rain barrels would make only a small dent (less than one percent) in residential outdoor water usage, and they would take up a lot of room.
Cisterns are a Better Solution
Cisterns do the job. I recently installed two 1,700-gallon underground cisterns on a 4,400 square foot lot in residential Sunnyvale. Each cistern is 5 feet tall by 5 feet wide by 13 feet long. It is much cheaper to store water in a tank above ground, as is often done in rural areas, but in a residential area with limited space, underground cisterns make the most sense. I hired professionals to dig the holes and lower the cisterns into place. I chose the five-foot-tall cisterns so the holes would not be too deep or costly.
Pipes connect all the downspouts and the patio to fill the cisterns. A pump in each cistern connects to the drip irrigation system, which delivers the water where and when it is needed. It is important to include a way to divert excess rainwater when the cisterns are full. My front yard has a reasonable slope; the cistern there overflows through an outlet pipe to the yard. The backyard cistern has a sump pump to pump overflow water to the street.
In Sunnyvale, no city permits are required to install or have a cistern, and this is probably true for most cities in the Bay Area. Local plumbing ordinances apply to connecting the irrigation system up to the city water supply.
The 3,400 gallon system filled up quickly with all the rain we had in 2010. The expectation is that this system will reduce outdoor water use by 7,500 to 22,500 gallons per year. That's a lot of water that will not come from California reservoirs via the delta or be pumped from underground aquifers. It's our family's most important contribution to reducing demand and the stress on California's water systems. It is great feeling to know you are watering your garden and flowers with rain captured and saved on your own roof.
John Cordes is tri-chair of the Chapter's Political Committee, a member of the Executive Committee, an ICO leader and Ski Touring section leader.