Rainwater is one of the cleanest and most abundant sources of water. A 1,000 square foot rooftop can potentially capture up to 13,000 gallons in an average water year in the Oakland/Berkeley area. Rainwater is ideal for watering vegetables and can even serve as an emergency water supply.
Although there is plenty of water from the sky even in a drought year, the real challenge is capturing enough water to irrigate gardens throughout the 5 month dry period of May through September. Rain is free, but rain water catchment systems can be expensive. Tanks alone cost from $0.50 to $2 per gallon, depending on the tank size and material. One cost-saving approach is to harvest rainwater in the soil using earthworks, which increase increases soil moisture content and provides plants with greater resilience during the dry season.
Another relatively inexpensive alternative to capturing rainwater in tanks is the installation of greywater reuse systems. The average person generates between 25-40 gallons of usable greywater every day. A family of four would generate about 3,900 gallons of greywater per month, which would be enough to irrigate about 4,600 square feet of a low water use garden during the peak water demand in July. With a little bit of plumbing and a relatively small investment of funds, greywater reuse offers a year-round source of irrigation for the urban landscape.
However, greywater is limited in its applications. According to the state water code, greywater needs to be distributed under 2 inches of mulch. Also, passive greywater systems rely on gravity for distribution, and if pumps are involved the costs and maintenance needs tend to go up.
In summary, both greywater and rainwater are important features of a drought resilient garden. Drought Smart works with clients in determining the best configuration of these technologies to come up with affordable and efficient solutions.