An estimated 371,000 Californians — about 1% of the state’s residents — rely on drinking water that may contain high levels of toxic chemicals such as arsenic, nitrate or hexavalent chromium, according to a study from the University of California campuses in Berkeley and Los Angeles.

In a news release issued Tuesday by UC Berkeley, researchers said the results of the study likely understate the number of people impacted by unsafe drinking water, as the study included just the three chemicals.