This map shows the approximate locations of community water systems in the San Joaquin Valley that were majority-Latino and had elevated levels of nitrate contamination of drinking water between 2003 and 2017. Community systems mainly serve places where people live, like cities and towns; they’re what most people think of as water utilities.
To be considered majority-Latino, these systems had to be located in a census block group determined by the 2018 American Community Survey to be at least 50 percent Latino. The eight counties in the San Joaquin Valley are Fresno, Kern, Kings, Madera, Merced, San Joaquin, Stanislaus and Tulare.
Clicking on a point brings up information for the census block group where the community water system is located, including the percent of the census block group that was Latino and its 2018 mean household income. The 2018 mean income for the state of California is also given so that each census block group’s mean income can be compared to it.
After the census demographic information is information about the community water systems – the name of the community water system, whether the system gets its drinking water from a groundwater or surface water source, and the population it serves. For each system, there is also a chart that shows the highest nitrate test per year, the average nitrate concentration per year and a reference line at 3 milligrams per liter, or mg/L.
The Environmental Protection Agency considers 3 mg/L of nitrate in groundwater used for drinking water an indication of contamination above naturally occurring levels. The map includes only systems with at least one test at or above that level. The pop-up box also includes a table with the total nitrate tests conducted by the system between 2003 and 2017 and the number at or above 3, 5 and 10 mg/L.
The water system data come from Freedom of Information Act requests fulfilled by the California State Water Resources Control Board. Some of the data can also be found on the U.S. Environmental Protection Agency’s Safe Drinking Water Information System website. The census block group data come from the 2018 American Community Survey.