<p>In California, mains water is delivered by local public water systems, regulated by the State Water Resources Control Board, Division of Drinking Water under the US EPA Safe Drinking Water Act. Typical hardness: Mostly hard; very hard in the south and Central Valley (Colorado River supply), softer in far-north / Sierra snowmelt areas. For a specific ZIP, see the EWG Tap Water Database.</p>
Sources: State Water Resources Control Board, Division of Drinking Water, EWG Tap Water Database