Untreated water can host plenty of harmful bacteria and viruses. That’s why starting in the early 1900s, U.S. cities began disinfecting their drinking water with chlorine. Afterward, rates of waterborne disease, such as cholera (KAH-lur-uh) and typhoid (TY-foid), dropped sharply. Typhoid, caused by a type of Salmonella bacteria, used to sicken one in every 1,000 people in 1900. By 2006, the rate was down to one in every million.
2) By-products of disinfection
Chlorine and bromine can kill many dangerous waterborne germs. But these disinfectants also can react with other chemicals in the water. The results may be new and dangerous by-products. One that can show up: chloroform. This chemical is toxic to the kidneys, liver and brain.
3) Industrial chemicals
Many companies use perfluorinated (Per-FLOR-ih-nay-ted) compounds, or PFCs, to make everything from nonstick coatings (like Teflon) to firefighting foams. They are so widely used that these chemicals have been showing up in water. They also are hard to remove from drinking water and hard to track.
With super-strong chemical bonds between their carbon and fluorine atoms, these pollutants won’t break down naturally in the environment. And water treatment plants were never designed to remove them.
Some research has linked PFCs to a higher risk of certain cancers, to learning problems, to growth deficits and to fertility problems. Close to 5,000 different PFCs exist today, very few of which are regulated, says Jamie DeWitt. She’s a toxicologist at East Carolina University in Greenville, N.C. Chemical companies are not required to report what they use if that chemical isn’t already regulated, she notes. In June 2018, a report by the U.S. Centers for Disease Control and Prevention suggested lowering exposure limits for some PFCs below current federal guidelines. Some states, including New Jersey and Vermont, have set such stricter limits.
Arsenic is a concern for the two in every 15 U.S. residents who draw their drinking water from private wells instead of city water systems. Arsenic occurs naturally. It also can get into groundwater from its use in agriculture or mining. Exposure to high levels of this element has been linked to skin, bladder and lung cancers. It also can lower IQ and trigger birth defects. An estimated 2 million people or more in the United States may be exposed to levels of arsenic above the federal limit of 10 parts per billion. That’s according to a 2017 report in Environmental Science and Technology.
Nitrates are commonly used as a plant fertilizer. So these pollutants can enter water when rains run off of farms and fertilized lawns. In excess, these chemicals can prevent red blood cells from carrying enough oxygen around the body. The Clean Water Act of 1972 limits factories from polluting waterways. Farms pollution, however, is largely unregulated.
Farming states like Iowa have been hardest hit by nitrate pollution, says Christopher Jones. He’s an engineer at the University of Iowa in Iowa City. Curbing this pollution has proven difficult. For instance, the Mississippi River is a source of drinking water for several U.S. states. Yet despite a decade of work to reduce nitrates entering this river, nitrate levels in waters getting Iowa runoff are consistently higher today than they were 20 years ago. Jones reported the finding in April 2018 in PLOS ONE.
Lead pipes still carry water within 11,000 U.S. communities. These provide tap water to some 15 million to 22 million people. That’s according to a 2016 survey by the American Water Works Association. Very acidic or corrosive water can leach lead from plumbing pipes. That’s why the EPA mandates that cities adjust water chemistry to minimize such leaching. But those control measures are not foolproof. For instance, the Flint, Mich., lead crisis occurred when the city switched to a more corrosive source of drinking water, but didn’t adjust the chemicals used to compensate. Some communities have committed to replacing every lead water line — a very costly measure.