According to a study from UC Berekely, more than 370,000 Californians have contaminated drinking water. The study found that populations reliant on domestic wells faced greater water quality concerns than those served by community water systems. Roughly 3.4% of Californians rely on domestic wells. The study found that poor water quality disproportionately impacts communities of color in California, with the highest estimated arsenic, nitrate, and Cr(VI) concentrations in areas of domestic well use.
The full study and report is available here: https://ajph.aphapublications.org/doi/full/10.2105/AJPH.2021.306561