California Code, Water Code - WAT § 56040

(a) The control of storm and other waste waters of or within said district, including waters which arise outside said district and which flow or drain into or through the said district;

(b) The protection from damage by storm or waste waters of private property and of public highways and other public property within said district;

(c) The conservation of storm and waste waters for beneficial and useful purposes by spreading, storing, retaining or causing such waters, or any part thereof, to percolate into the soil within or without said district or the saving and conservation in any manner of any and all of such waters.