October 2017 - The water system of Brownsville, Texas, with one of the highest poverty rates in the US, is the largest US water utilities with the worst water quality. Testing in 2015 revealed 12 contaminants above established health guidelines. Among those contaminants, the highest abnormality was arsenic, a naturally occurring mineral that causes bladder, lung and skin cancer, as well as harm to the skin and lungs. Arsenic levels in Brownsville's water supply—serving 176,000 people—were 700 times greater than established health guidelines.

The data comes from the Environmental Working Group (EWG) which compiled 28 million water records collected from about 50,000 water utilities that serve a total of 280 million Americans, or nearly 90 percent of the US population.

In contrast to Brownsville, the Massapequa Water District in New York, serving 43,000 people, is the largest among the 26 water utilities for which no contaminants were detected above health guidelines.

While most of the detected contaminants were at legal levels, these levels still pose health risks, according to authoritative scientific studies. About 81 percent of US water systems contain pollutants linked to cancer, according to EGW. In addition, 77 percent of Americans drink water containing hexavalent chromium—linked to liver and the reproductive system damage—while lead was detected at levels that may be harmful to children at 19,000 water utilities.

US farming practices pose another potential threat to US water safety. About 7 million Americans drink water containing an unsafe amount of nitrate, a fertilizer used mostly in corn planting in the US and one of the most common contaminants in drinking water.

Of those exposed, 700,000 live in Iowa , the largest producer of corn in the US, according to 2017 data from USDA . In Iowa, 13.5 million acres (38% of the state's land area) are planted with corn, with about 95 percent of the area fertilized by nitrogen

The distinction between legal and healthy levels of contaminants is worth the attention of every citizen that relies on piped drinking water. Recent headlines from Flint, Michigan, clearly could emerge from many water utility areas around the US. As mentioned, Iowa is a useful case example.