This map shows the approximate locations of community water systems in each of the 10 states – California, Illinois, Iowa, Kansas, Maryland, Nebraska, Oklahoma, Pennsylvania, Texas and Wisconsin – where nitrate contamination of drinking water got worse between 2003 and 2017. The Oklahoma map has systems with worsening nitrate between 2007 and 2017. A community system is what most people think of as a water utility, mainly serving places where people live, such as cities and towns.
Clicking on a point brings up the name of the community water system, whether the system gets its drinking water from a groundwater or surface water source, the population served by the system, and whether the system is in an urban area. (If the “Urban area” field says “No,” this means the system is in a rural area.) Each system also has 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 final component of each pop-up box is 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 data were obtained by EWG under each state’s public records law. Some of the data can also be found on the EPA’s Safe Drinking Water Information System website.
To see the methods used for this study, click here.