California Code, Water Code - WAT § 10571

(a) As California has grown and developed, the amount of stormwater flowing off buildings, parking lots, roads, and other impervious surfaces into surface water streams, flood channels, and storm sewers has increased, thereby reducing the volume of water allowed to infiltrate into groundwater aquifers and increasing water and pollution flowing to the ocean and other surface waters. At the same time, recurring droughts and water shortages in California have made local water supply augmentation and water conservation efforts a priority.

(b) Historical patterns of precipitation are predicted to change, with two major implications for water supply. First, an increasing amount of California's water is predicted to fall not as snow in the mountains, but as rain in other areas of the state. This will likely have a profound and transforming effect on California's hydrologic cycle and much of that water will no longer be captured by California's reservoirs, many of which are located to capture snowmelt. Second, runoff resulting from snowmelt is predicted to occur progressively earlier in the year, and reservoirs operated for flood control purposes must release water early in the season to protect against later storms, thereby reducing the amount of early season snowmelt that can be stored.

(c) Rainwater and stormwater, captured and properly managed, can contribute significantly to local water supplies by infiltrating and recharging groundwater aquifers, thereby increasing available supplies of drinking water. In addition, the onsite capture, storage, and use of rainwater for nonpotable uses significantly reduces demand for potable water, contributing to the statutory objective of a 20-percent reduction in urban per capita water use in California by December 31, 2020.

(d) Expanding opportunities for rainwater capture to augment water supply will require efforts at all levels, from individual landowners to state and local agencies and watershed managers.