How much can a water filter do?

In recent years, water safety crises have occurred in several cities, including Baltimore, Flint, Mich.Jackson, Miss., and Newark, NJ, where lead or bacteria have leached into tap water, forcing people to rely on bottled water or boiling tap water to rid it of pathogens.

In Wilmington, NC, high levels of perfluoroalkyl and polyfluoroalkyl chemicals commonly known as PFAS were detected in the local watershed. PFAS have been linked to numerous health problems, including cancer, liver damage, and fertility problems. The Environmental Protection Agency proposed new regulations in March that would reduce drinking water levels of six types of PFAS, significantly lowering allowable detectable amounts. (Drinking water is not the only source of exposure to PFAS, which can be found in food packaging, cooking pots, and waterproof clothing, among other sources, but it is recommended that contact be reduced where possible.)

These events raise questions about how safe municipal water supplies are in the United States and whether additional filtration steps are needed, even outside areas experiencing acute crisis. And if so, are there any home water filters that can help?

Problems with the system

Water purification is often cited as one of the greatest health improvements of the 20th century, and has contributed significantly to it lower the mortality rate of infectious diseases. Water safety standards were established in the Safe Drinking Water Act of 1974, which empowers the EPA to limit the amounts of many metals, bacteria, pesticides and other harmful contaminants that can be detected in water. Government agencies monitor water treatment plants to ensure they comply with the law, and if violations occur, they must notify consumers within 24 hours. (Owners of private wells are responsible for keeping their water free from contaminants.)

However, since the introduction of the Safe Drinking Water Act, other problems with water monitoring have arisen. For example, most water treatment plants aren’t set up to remove more modern contaminants, such as PFAS, pharmaceutical drugs and endocrine-disrupting chemicals, said Detlef Knappe, a professor of civil, construction and environmental engineering at North Carolina State University, who was one of the first to on the Wilmington PFAS problem.

Another concern is whether we are “setting standards at a rate that reflects what we know about the science of our water,” said David Cwiertny, a professor of civil and environmental engineering at the University of Iowa. He gave the example of nitrate, an agricultural pollutant present in the water supply DesMoines. As the local water treatment plant takes steps to remove the contamination, there are questions about whether the permitted levels can still be met cause health damage.

Outdated infrastructure is also a problem. In several of the recent crises, contamination occurred when lead leached into the water as it passed through the distribution lines. National regulations on the amount of lead allowed in pipes have tightened over the years, but many old water distribution systems have not been updated and contain unsafe levels.

“Often things go wrong because of a lack of investment in this kind of infrastructure,” said Dr. Handsome. “The rate at which we replace the distribution pipes in the network is not keeping pace with the rate at which the system actually needs to be maintained.”

Finally, experts say that water treatment plants are not equipped for the extreme weather events that climate change is making more common. That was part of the problem in Jackson, where flooding from heavy rains inundated one of the city’s treatment plants, sending untreated, bacteria-laden water into people’s homes.

The crises in Flint, Baltimore, Jackson and Newark are exceptional cases right now — the public water supply in the U.S. is generally safe, said Thanh Nguyen, a professor of civil and environmental engineering at the University of Illinois, Urbana-Champaign. But “the number of exceptions could increase over time if we don’t update the infrastructure,” she said.

What home filters can do

If there is a known crisis in your area, local officials will make recommendations on how best to protect yourself. If you’re generally concerned about potential contaminants, home water filters can help with some issues.

Most filters contain activated carbon to trap contaminant particles, which can be used in pitchers, refrigerator dispensers, faucet attachments, or systems installed under the sink. Activated carbon is good at removing many chemicals and metals, but not all of them (it doesn’t hold nitrates, for example), and it can’t filter out most bacteria.

The American National Standards Institute and NSF International – two independent groups that evaluate product performance – have established standards for water filters. Companies are not required to make products that meet NSF/ANSI standards, but because “there is no federally regulated requirement,” certification can help “ensure that the product is not counterfeit or is actually effective,” according to Kyle Postmus, senior manager of the Global Water Division at NSF.

NSF/ANSI Standard 42 is for aesthetics, such as taste, smell and appearance (people often want to filter out traces of the disinfectant chlorine). Standard 53 focuses on safety, ensuring that levels of lead or mercury, as well as some pesticides and industrial chemicals, remain below accepted limits. The certifications are for individual contaminants and the product must specify all contaminants for which it is approved.

Home filters seem to work quite well for PFAS and can now be NSF/ANSI Standard 53 certified for some of those chemicals as well. In a study published in 2020, Dr. Handsome and his co-authors found that pitcher and refrigerator filters that use activated charcoal reduced PFAS levels by about 50 percent on average. More advanced filtration systems using a process known as reverse osmosis were more than 90 percent effective, but they are much more expensive and waste a significant amount of water.

Sometimes filters can do more harm than good. The research of Dr. Nguyen revealed that if water sits in a tap or a filter under the sink for long periods of time, such as overnight, it can actually picking up more contaminants, including lead and bacteria. That’s because the water is essentially bathed in high concentrations of the particles trapped by the activated carbon. When the faucet is turned back on, the pollutant-infused water comes out. That’s why Dr. Nguyen that it’s important to flush your water filter for at least 10 seconds before drinking from it. Also, make sure to replace your filter regularly.

Most of the experts interviewed for this article said they used a home filter, but none said it was essential. Some used filters for taste issues, while others said it was a precaution. “Not everyone needs them, but I can think of a lot of reasons why people might,” said Dr. Cwiertny. “What I would encourage is that people make informed decisions and know why they are buying a device” – for example, for a specific taste problem or for filtering out a known contaminant.

If you are concerned about the quality of your water and want to know if you should invest in a filter, you can use a home test kit. You can also use one Consumer confidence report of the EPA that will describe what’s in the water as it leaves your local treatment plant, though the report doesn’t take into account what the water might encounter as it flows through the distribution pipe network.

The experts warned that if your area has a known problem with lead or some other contaminant, a filter is a bandage on a wound that needs surgery — the bigger problem with the pipes or water supply has yet to be addressed.