Americans have a lot of questions about their drinking water. How is it treated? What’s in it? Most importantly, is it safe?
“I’ve even been out to eat where people overhear me talking about my work and come over to ask me a question about their tap water,” said Kimberly Parker, an environmental engineer who studies chemical contaminants in drinking water at Washington University in St Louis.
Most Americans have access to municipal water, which “tends to be really well treated” and largely safe to drink, said Parker. Across the US, water is monitored for contamination via centralized infrastructure at federal and state levels.
In Parker’s experience, “many environmental engineers choose not to use filtered water” because of their informed confidence in the safety of tap water, she said.
Nevertheless, whether you’re drinking municipally treated water or relying on a well, there are water-safety challenges.
“There has been a myth in the United States that drinking water is safe for everyone,” said Yolanda McDonald, lead investigator of the Drinking Water Justice Lab at Vanderbilt University. “We know that’s not true.” Her work maps where US drinking water fails to meet federal standards, including Flint, Michigan, and Jackson, Mississippi, where communities have suffered from water sector failures.
There’s no one-size-fits-all way to ensure your drinking water is safe. Whether you need to worry about your tap water and what you should do to purify it depends on three things: what’s in your water, where it comes from and your own health.
What contaminants most commonly affect US drinking water?
Water treatment plants test drinking water for more than 90 contaminants before releasing it into the network of mains and pipes that lead to your tap. But tap water may still contain herbicides and pesticides, industrial pollutants, Pfas and heavy metals.
The US Geological Survey estimates 45% of America’s tap water is contaminated with Pfas, and well water is particularly vulnerable to nitrate pollution from agricultural chemicals. One type of pollutant, trihalomethanes (THMs), are actually a byproduct of the tap water treatment process, making them a relatively common issue.
In the US, water treatment plants use chlorine to prevent life-threatening waterborne illnesses caused by viruses, bacteria and protozoa in drinking water – cholera is one well-known example. However, the disinfection process creates THMs, which form when the chlorine reacts with organic matter in the water, such as leaf litter, said Parker.
While the Environmental Protection Agency (EPA) does not consider short-term or low-level exposure to THMs dangerous, when chronically present in drinking water in concentrations over 80 parts per billion (ppb) it’s “possibly carcinogenic”, according to the Massachusetts department of environmental protection. They may also pose risks to the liver, kidneys and reproductive system, though these effects are still being studied.
The vast majority of US water utilities are in compliance with the EPA’s Safe Drinking Water Act, said Parker. “When violations do occur, disinfection by-products, including THMs, are one of the most common causes.”
Lead, a neurotoxin, can also be a serious issue, as no level is safe to consume. Under the Biden administration, the EPA estimated 9m lead service lines were still in use in America, though in Trump’s second term that estimate dropped to 4m based on alternate data some watchdogs have questioned. Lead pipes represent a huge infrastructure issue. “Every day throughout the United States, there are communities where our pipes do need to be replaced,” said McDonald.
How do I test my drinking water?
Start by looking up your city or county’s local Consumer Confidence Report, a water safety document the EPA requires all municipal water systems to produce. It typically publishes readings from water leaving municipal facilities and tap water in government-owned buildings like libraries and fire stations.
The Safe Drinking Water Information System provides granular information about specific water systems, such as field reports that summarize inspection findings, and regulatory violation notices that flag issues like lead or excess chlorine in the water.
You can get your home tap water tested by a state-certified laboratory in your area – the EPA offers guidance on how to do this.
If you are a homeowner and your property was built before the 1990s, it’s important to establish whether you have lead pipes, said McDonald – if so, you are solely responsible for replacing them, or you may want to filter your water accordingly.
What kind of water filter should I get?
If there are any “contaminant exceedances in your area”, said Parker, pick the type of filter that will work for the specific issue. Some filter for germs but not chemicals, or vice versa.
“A lot of people are really worried about lead, but some popular filters you can buy don’t treat lead,” said Parker. Reverse osmosis filters, for example, have been found to be one of the most effective at removing Pfas, lead and THMs from water.
Look for filters certified by the National Sanitation Foundation, a non-profit that ensures high consumer standards for water purification products.
Consider your budget when it comes to the price, replacement parts and maintenance costs. Additionally, be realistic about how often you’ll replace the filter. Point of entry filters that handle all the water for a building, faucet-mounted filters and countertop carafes all have different purposes, requirements and pricing.
“These filters don’t work forever,” said Parker. “They’re like a sponge, and once that capacity is exceeded, it won’t work any more for that contaminant. So it’s important that you do read the filter instructions and understand how to use the filter correctly … because otherwise you’re just not getting that benefit,” she said.
Typically, pitcher-style filters are most accessible and affordable but require filter replacement every couple of months. On the other end of the price spectrum, residential reverse osmosis membranes and whole-house carbon filters cost more upfront but require less replacement (about annually for filters, and three to five years for the filter membrane itself).
One easy tip for reducing your chances of drinking contaminated water: run the tap if you haven’t been home for a while, or if you’re visiting a property you’re not familiar with, like a rental apartment. “Lead concentrations can build up in that stagnant water that’s just been sitting in the pipe,” along with other contaminants, Parker said.
How do wells affect water safety?
For the roughly 43 million Americans who rely on private wells, there is no federal monitoring requirement or any equivalent for the Consumer Confidence Report.
Well water “doesn’t necessarily go through a water treatment facility”, said Yoram Cohen, a distinguished professor of chemical and biomolecular engineering at the University of California Los Angeles, who runs a leading research program in remotely monitored reverse-osmosis water purification.
Well users are often exposed to the same contaminants that threaten municipal systems, plus others that are location-specific, which could include agricultural nitrates, naturally occurring arsenic, chromium and salinity, said Cohen.
Because every well is different, Parker recommends privatewellclass.org, a resource featuring location-specific guidance on testing and maintenance from researchers at the University of Illinois Urbana-Champaign.
Who should be particularly cautious about their water?
Some filtering decisions have to do with an individual’s personal health concerns.
McDonald learned this first-hand when her husband, who has chronic kidney disease, kept exhibiting elevated phosphorus levels despite dietary changes. Phosphorus isn’t a contaminant the federal government regulates, because most people tolerate higher levels safely.
“As a water researcher, it dawned on me: ‘I wonder if the phosphorus is coming from the water,’” said McDonald. A test confirmed her suspicion. Using a targeted filter, they were able to reduce her husband’s phosphorus levels.
People should “consult with their physician about what type of water they’re drinking” and whether it may interact with their personal health concerns, said Daniel Giammar, principal investigator at Trusted Tap, a water safety program run by Washington University in St Louis and the University of Illinois. “Hard” water typically contains more calcium and magnesium, which aren’t a health risk to most – in fact, the extra minerals can be good for you – but some people may nonetheless prefer “soft” water, which is lower in minerals and less drying on skin and hair.
“I know people with kidney stones who choose to soften their water because they don’t want the high calcium,” which can worsen their condition – though it’s perfectly safe for others, he said. Others may choose to filter out calcium and magnesium in “hard” water because they simply prefer the taste.
