The Elemental Guide to Water

How Safe Is Your Tap Water?

The answer is murky

This story is part of The Elemental Guide to Water, a five-part special report on the health benefits of water, the science behind seltzer, the truth about fancy H2O, the safety of tap water, and how much water you really need to drink.

Tap water is a modern marvel. Unless you’re an octogenarian, you probably don’t know any other way. With just the turn of a faucet, Americans have access to H2O. But is it safe to drink?

In cities like Flint, Pittsburgh, Milwaukee, Detroit, Newark, and others, where improperly treated water and aging pipes have been responsible for leaking lead and copper into the drinking water supplies, the answer is no — the tap water has been found to be downright dangerous. These tragedies have raised questions and distrust about the cleanliness of tap water everywhere.

Cities routinely test tap water for viruses like cryptosporidium and giardia and disinfect, filter, and remove many pathogens, but there are still a myriad of contaminants that can remain — many of them legal. Federal authorities argue that there can be trace amounts of pollutants in water that do not always present a risk to health. But larger water violations are common, and one 2018 study looking at data from 1982 to 2015 reported that between 9 million and 45 million Americans may have been exposed to drinking water from sources that do not meet current Environmental Protection Agency (EPA) standards for safety.

So in other words, it’s a murky subject. Here’s what you should know.

How tap water is regulated

Tap water makes it to your home through a process that involves taking groundwater, river, or runoff water sources, then piping that supply and storing it in a reservoir or water tower where it’s treated, filtered, and regularly tested for bacteria and chemicals. According to the Natural Resources Defense Council, city taps are tested 100 or more times a month. That water is then delivered via aqueducts and wells to homes and businesses.

The EPA is the government agency responsible for setting the legal limits for contaminants in tap water and overseeing overall water quality. Even if…