The majority of residents in the San Joaquin Valley rely on groundwater for some or all of their drinking water, and many California groundwater basins are contaminated with a mix of manmade and naturally occurring toxicants.
California set the drinking water standard for nitrate in 1962 and has regulated water quality since 1969.
The San Joaquin Valley is particularly hard hit by nitrate: 63 percent of the state’s public water systems that report violations of health standards for the contaminant in 2015 were in the Valley.
"Nitrate is the most critical, the most immediate contaminant in the San Joaquin Valley," Harter says.
State regulators are in the second year of a program to help keep agricultural nitrate out of groundwater in the Central Valley.
Other major human sources of groundwater contaminants in the San Joaquin Valley include pesticides that are banned but still linger in the environment.
The San Joaquin Valley has three of the four California counties with the highest DBCP levels, which are triple that deemed to be safe by the state.
In 2015, 60 percent of the state’s public water systems reporting health violations for arsenic were in the Valley, and Madera County drinking water has the highest levels of arsenic statewide.
He only found out when he started working as policy director at the Community Water Center, which advocates for safe drinking water in the San Joaquin Valley, and he realized his town was one that had found the contaminant in its drinking water.
"We don’t know how air pollution impacts the body differently from water pollution or how multiple effects work out," Capitman says.