It can be difficult to find direct linkages between illness and wastewater-polluted waters, but a study looking at emergency room visits for gastrointestinal illness did just that. Over a four-year period, scientists compared hospital records in parts of Massachusetts with and without combined sewer overflow (CSO) systems (Jagai et al., 2015). The authors found that only people living in areas with CSOs that discharge to drinking water sources (i.e., people who could have been exposed to wastewater-polluted waters) were at elevated risk for gastrointestinal illness up to eight days after heavy or extreme precipitation.
In addition to pathogens, nitrates are common components of wastewater, even when treated, that find their way into drinking water. Elevated nitrate levels are known to cause methemoglobinemia, commonly known as blue baby syndrome (Greer & Shannon, 2005), and recent studies have linked nitrates in drinking water to colon, ovarian, thyroid, kidney, and bladder cancer in adults (Ward et al., 2018). In fact, numerous studies have shown that increased risk of cancer occurs with nitrates at levels below the U.S. standard of 10 parts per million (Temkin et al., 2019; Ward et al., 2018). A Danish study reported increased risk of colon cancer with nitrate levels above 3.87 parts per million (Schullehner et al., 2018).