Riverside's water supply begins as pure rain and snow which is naturally filtered through the sand and gravel of the Bunker Hill and Riverside Basins in San Bernardino and Riverside. This water settles in pools deep in the earth and are then tapped for domestic use by 51 wells operated by Riverside Public Utilities.

In 2002, Riverside met 99.0 percent of its water needs from underground resources receiving only 1 percent from Western Municipal Water District. Water quality information for imported water is available on request.