California utilities with very hard water.
Above 180 mg/L (10.5 grains per gallon). 718 utilities serving 5.6 million people as they report it, largest first.
401 to 500 of 718, by people served
Source: California State Water Resources Control Board, Division of Drinking Water, 2,449 utilities, results from Jan. 2, 2019 to July 14, 2026, read Oct. 10, 2026. Each sampling point is taken at its median; a figure is typical where every point falls in one band.
Also: 7 utilities’ own water quality reports, read by hand, each named on the utility’s page.
Bands are the U.S. Geological Survey’s, at 17.1 mg/L to the grain. People served is what each utility reports; where one sells water to another, the same people can be counted twice. How hardness is measured here.
Where to go next
- California hardnessEvery band in the state, with the largest utilities in each.California water hardness
- Softeners comparedCertified softeners and what each costs over five years, salt included, at your water’s hardness.Softeners, salt included
- Hardness across the USEvery state with hardness results, and the hardest and softest large utilities.US water hardness