A new study led by a team of researchers from the University of California Berkeley and the University of California Los Angeles has revealed that approximately 370,000 Californians may be exposed to unsafe levels of arsenic, nitrate or hexavalent chromium in their drinking water, and that people of color are more likely to be effected. However, the number of people across the state that rely on unsafe drinking water could be much higher since the study only focuses on the three most common contaminants, and does not take other potentially harmful drinking water contaminants into account.

Since 2012 the state of California has acknowledged that access to an affordable source of clean and safe drinking water is a basic human right. As such, federal water regulations require water utilities to regularly test drinking water to ensure levels of harmful contaminants do not exceed drinking water quality health standards. However, many water systems supplying drinking water to communities in California do not meet the required drinking water standards. Furthermore, many rural households depend on unregulated private wells for their drinking water.

A study, which was recently published in the American Journal of Public Health, has quantified concentrations of three key drinking water contaminants: arsenic, nitrate, and hexavalent chromium, in both community water supplies and private wells across California, analyzing demographic disparities in the quality of drinking water supplied to households across the state.

According to the authors, it will become increasingly more urgent to address the inequities with regard to access to clean, safe drinking water as climate change impacts such as prolonged periods of drought and water scarcity become more apparent. This study shows that a large number of Californians who depend on private wells for drinking water are likely being exposed to high levels of harmful contaminants, and pinpoints locations where water quality assessments should be targeted to ensure that the basic human right to access to clean safe water is met.

For their study, the researchers focused the three most prevalent toxic chemicals found in drinking water across the state of California. Arsenic occurs naturally in groundwater, but can become more concentrated as groundwater is depleted and the water table decreases. Nitrate originates primarily from agricultural sources such as fertilizer runoff or animal waste from large scale animal production. Hexavalent chromium originates from industrial activities and manufacturing plants.

According to the study, around 1.3 million people — or three and a half percent of the Californian populace — depend on private wells for their drinking water. Of the 370,000 people whose drinking water is contaminated with arsenic, nitrate or hexavalent chromium, over 150,000 receive their water from private wells for which there is very little data regarding water quality. According to the researchers, it is crucial that the gap in this data is filled so that all Californians can get a clearer understanding of what contaminants they are in their drinking water, and whether it's safe to drink.

The researchers in collaboration with scientists from the California Environmental Protection Agency (CalEPA) and the Community Water Center, have produced an online Drinking Water Tool to help residents and policymakers assess the source of drinking water supplies and pin-point areas in California where the groundwater is likely to contain high levels of arsenic, nitrate, hexavalent chromium and 1,2,3-Trichrolopropane that are deemed unsafe.

"The goal of the Drinking Water Tool is to provide timely access to data that can inform efforts to protect the state's drinking water and groundwater supplies, particularly in disadvantaged communities where the threats are greatest," said Clare Pace, a postdoctoral scientist at UC Berkeley and lead author of the study. "We'd like to continue to refine the Drinking Water Tool in collaboration with the Community Water Center and in response to feedback from other organizations and decision-makers who can help ground-truth the data."

The online Drinking Water Tool lets users compare water quality information of groundwater and drinking water against community demographic data across California. It also gives users some insight into how drought conditions could affect water availability for people that depend on private wells for their drinking water, and those that get their water from smaller community water systems serving less that 10,000 residents.

"In this era of climate change, our groundwater is becoming an increasingly precious resource, and we're facing historic levels of drought and well failures. Even if a well doesn't fail, drawdown of the water table can impact water quality by concentrating contaminants, making these problems even worse," Cushing said.

Journal Reference:

Clare Pace, Carolina Balazs, Komal Bangia, Nicholas Depsky, Adriana Renteria, Rachel Morello-Frosch, Lara J. Cushing. Inequities in Drinking Water Quality Among Domestic Well Communities and Community Water Systems, California, 2011‒2019. American Journal of Public Health, 2022; 112 (1): 88 DOI: 10.2105/AJPH.2021.306561