Each point on the map shows one of the 1,695 community water systems that served 25,000 people or less and had a 2016-2017 average nitrate concentration in their drinking water of 5 parts per million, or ppm, or more. The light-colored points are systems with two-year average nitrate values between five and just less than 10 ppm, and the darker points are systems with nitrate levels at or above 10 ppm. Click on a point to see more information about the water system. This information comes from the EPA’s Safe Drinking Water Information System.
Water systems must adhere to a legal limit of 10 ppm for nitrate in drinking water. Levels at or above 10 ppm are associated with so-called blue baby syndrome, a potentially fatal condition that starves infants of oxygen. But newer studies have shown increased risks of cancer and birth defects at 5 ppm or even lower levels.
Community water system points also include county-level fertilizer and manure application information. Clicking on a location will provide the number of acres in that county that were treated with fertilizer or manure and the total cropped or pastured area. Fertilizer or manure was applied to more than 281 million acres across the country in 2017. This information comes from the 2017 USDA Census of Agriculture.