BERKELEY (CBS SF/BCN) — According to University of California researchers, an estimated 371,000 Californians rely on drinking water that may contain high levels of toxic chemicals such as arsenic, nitrate or hexavalent chromium.

The study, published in the current edition of the American Journal of Public Health, was the first to quantify the average concentrations of multiple chemical contaminants in both community water systems and domestic well areas statewide.

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“Our data strongly indicate that a large number of people who rely on domestic wells are likely drinking water with high levels of contaminants and suggest locations where we should begin targeted assessments to ensure that the human right to water is fully implemented,” said Rachel Morello-Frosch, a professor of public health and of environmental science, policy and management at UC Berkeley.

The study focused on three chemical contaminants based on their prevalence in the state, as well as on their known toxicity — arsenic, nitrates and hexavalent chromium.

Researchers said that arsenic was chosen because it is found naturally in groundwater and can be concentrated by depletion of the water table.

Nitrate contamination of groundwater is common in agricultural regions due to fertilizer runoff and industrial animal farming while hexavalent chromium is produced by industrial and manufacturing activities.

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The team also released an online Drinking Water Tool (drinkingwatertool.communitywatercenter.org/) that policymakers and members of the public can use to look up where their water comes from, as well as map areas of the state where groundwater sources are likely contaminated with unsafe levels of arsenic, nitrate, hexavalent chromium and 1,2,3-Trichlorolopropane.

Researchers combined data on the state’s community water systems, domestic well permits, residential tax parcels, building footprints and census results to locate California households likely to be served by unregulated domestic wells.

Then they used measurements of drinking water and groundwater contamination throughout the state to estimate contaminant levels for those served by both community water systems and domestic wells.

“I think a lot of people might be surprised to learn that, given how wealthy the state of California is, we still don’t have universal access to clean drinking water,” said study co-author Lara Cushing, an assistant professor of environmental health sciences at UCLA. “For the three chemical contaminants that we looked at, we found that places with a higher proportion of people of color experienced greater levels of drinking water contamination.”

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