Water safety crises have cropped up throughout the United States over the past few years. So how much do home water filters help?  Here's what you need to know, according to the New York Times' "Well."

The problems with municipal water systems

In 1974, the Safe Drinking Water Act was passed, giving the Environmental Protection Agency power to restrict how much metals, bacteria, pesticides, and other contaminants can be detected in water, Smith reports. However, since then, some water-monitoring issues have arisen.

According to Detlef Knappe, a professor of civil, construction, and environmental engineering at North Carolina State University, most water treatment plants aren't set up to remove more modern contaminants, like pharmaceutical drugs and polyfluoroalkyl substances (PFAS), which have been linked to a variety of health problems including cancer, liver damage, and fertility problems.

David Cwiertny, a professor of civil and environmental engineering at that University of Iowa, also raised the concern over whether the United States is "setting standards at a pace that is reflective of what we know about the science of our water." Cwiertny provided the example of nitrate, an agricultural pollutant present in the water supply in Des Moines, Iowa. While water treatment plants work to remove the contaminant, there are questions that remain about whether allowable levels still cause health problems.

There's also the issue of aging infrastructure, Smith reports. In a number of recent water crises, contamination occurred when lead reached water as it traveled through distribution pipes.

"Often, things go wrong because of just underinvestment into this type of infrastructure," Knappe said. "The rate at which we're replacing the distribution system pipes in the network is not keeping up with the rate at which the system really needs to be maintained."

Experts also say water treatment plants aren't equipped to manage extreme weather events that have become more common as a result of climate change. This was part of the water crisis in Jackson, Mississippi, when flooding overpowered one of the city's treatment plants, allowing untreated water to travel to people's homes.

How at-home filters can help

Most at-home water filters contain activated carbon to capture contaminant particles, Smith reports. While activated carbon is good at removing many chemicals and metals, it doesn't remove all of them and can't filter out most bacteria.

Two groups — the American National Standards Institute (ANSI) and NSF International — have established standards for water filters. And while companies aren't required to make their products meet those standards since "there is no federally regulated requirement," certification can help to "ensure that the product isn't a counterfeit or it's actually effective," according to Kyle Postmus, senior manager of the Global Water Division at NSF.

Research has found that home filters work relatively well at filtering out PFAS and can be NSF/ANSI certified under Standard 53, which ensures levels of different contaminants are below the accepted limit. In a 2020 study, Knappe and colleagues found that on average, pitcher and refrigerator filters using activated carbon reduced PFAS levels by around 50%. More advanced filtration systems using reverse osmosis were more than 90% effective, but are much more expensive and waste a large amount of water.

However, sometimes filters can do more harm than good, Smith reports. Research from Thanh Nguyen, a professor of civil and environmental engineering at the University of Illinois, Urbana-Champaign, found that if water sits in a faucet or under-sink filter for a long time, it can pick up more contaminants, including lead and bacteria. As a result, Nguyen recommends you flush your water filter for at least 10 seconds before drinking from it.

Most experts interviewed by Smith said they use an at-home filter, but none said it was essential that everyone use one. "Not everybody needs them, but I can think of a lot of reasons why people might," Cwiertny said. "What I would encourage is that people make informed decisions and know why they're purchasing a device," whether that's for a specific taste or filtering out a known contaminant. (Smith, New York Times, "Well," 5/30)