Why Filter Drinking Water? What the Latest EPA and CDC Data Show

EPA counted 6,045 public water systems in the U.S. that were reported to have violated a health-based drinking water standard in 2023, out of 148,541 active systems that year. That gap is most of the answer to why filter drinking water at all. Private wells sit outside that system entirely, because the quality and safety of drinking water from private domestic wells are not regulated by the Federal Government under the Safe Drinking Water Act.

Filtering is not automatic, though. According to the CDC, if your tap water does not contain harmful germs or chemicals, you may not need a filter, because filters strip useful chemicals from treated water too. The sections below cover the reasons that hold up under the data: germs, lead, PFAS, disinfection byproducts and arsenic, private wells and bottled water, plus what filters cannot remove and how to match one to your water.

Key Takeaways

• According to EPA, 6,045 public water systems violated a health-based drinking water standard in 2023, while 29,703 failed at least one monitoring or reporting requirement.
• Drinking water accounted for 16% of waterborne illnesses but caused 40% of hospitalizations and 50% of deaths in a CDC journal estimate.
• Per EPA estimates, there are 4 million lead service lines across the country, based on 2025 data.
• According to USGS, at least 45% of the nation’s tap water has one or more types of PFAS.
• Around 15% of the U.S. population, over 43 million people, rely on private wells, which federal drinking water rules do not cover.
• Per NC State research, carbon pitcher and refrigerator filters reduced PFAS levels by about 50% on average, while reverse osmosis systems were over 90% effective.

Why filter drinking water?

You filter drinking water to remove a contaminant your supply actually carries, or to improve its taste. According to the CDC, water filters can improve the taste of water, the safety of water, or both.

A CDC journal study adds that transmission of disease via drinking water systems still occurs, often attributable to aging infrastructure, operational challenges, and private or unregulated water systems, such as private wells, that serve an estimated 43 million persons.

Source: EPA 2023 to 2025, USGS 2023, CDC Emerging Infectious Diseases 2023

Each row is a reason to check your own water; none of them tells you what your own tap carries. CDC cautions that taste, smell, and appearance are not always good indicators of water safety, so the case for a filter comes from a test or a report rather than from the glass.

Is filtered water really necessary?

Not for every household. CDC says if your tap water is already free from harmful germs and chemicals, you may not want to filter it, since filters remove beneficial chemicals along with harmful ones. A filter becomes necessary when a utility report or well test shows a contaminant, and the model you buy is certified to remove it.

How Often US Tap Water Breaks Health Standards

Most public water systems meet federal standards in a given year, but not all of them.

Per EPA’s compliance report, 107,559 of the PWSs active in 2023 had no reported violations of drinking water standards, while 6,045 were reported to have violated a health-based drinking water standard, meaning a contaminant was detected in excess of allowable limits or treatment technique requirements were not met.

That is about 4% of active systems. A wider count, 40,982 systems, violated at least one drinking water standard of any kind in 2023. The full breakdown sits in EPA’s national public water systems compliance report.

Enforcement falls hardest on small utilities: in 2023, 5,018 (3.4%) PWSs were an enforcement priority in at least one quarter of the year, and the majority (4,667 or 93%) of PWSs in enforcement priority status were small systems serving a population of 3,300 or less.

Why it matters: EPA found that 29,703 PWSs failed to meet at least one monitoring or reporting requirement, with the result that information about what contaminants were present in their drinking water was late, incomplete, or not reported at all. A clean annual report from one of those systems says less than it appears to.

What happens if you drink water that isn’t filtered?

On a public system that meets its standards, unfiltered tap water is already treated water. CDC says your utility’s annual water quality report will show if there are harmful germs or chemicals in your water. The risk sits with the exceptions: a health-based violation, a lead service line, or a private well nobody has tested.

Germs in Drinking Water and Waterborne Illness

A study in CDC’s Emerging Infectious Diseases journal found that an estimated 7.15 million domestically acquired waterborne illnesses occur in the United States each year. It notes that this estimate includes drinking, recreational, and environmental water exposures. The same model counted 118,000 hospitalizations and 6,630 deaths a year.

A later study in the same journal split that burden by exposure route. Of the estimated 7.15 million infectious waterborne illnesses in 2014, 16% were attributed to drinking water, but drinking water exposure caused 40% of hospitalizations and 50% of deaths. Recreational water carried the most illnesses (78%), but a smaller share of hospitalizations (36%) and deaths (20%). Other water contact, neither recreational nor drinking, made up the remaining 6% of illnesses, 24% of hospitalizations, and 30% of deaths.

The severe cases trace more to plumbing than to the treatment plant. Pathogens found in biofilms, such as nontuberculous mycobacteria (NTM) and Legionella bacteria, are predominant causes of hospitalizations and deaths from waterborne diseases in the United States. That matters for filter choice, because most home water filters, like pitcher or fridge filters, are not designed to remove germs from your water.

Weakened immune systems: CDC says if you have a weakened immune system, you are more likely to get sick from germs in water, and the parasite Cryptosporidium may make you sick. The agency also advises that if you have a weakened immune system, avoid changing water filters yourself, since used cartridges hold what they caught.

By the numbers: Globally, WHO and UNICEF report that 1 in 4, or 2.1 billion people, still lack access to safely managed drinking water, including 106 million who drink directly from untreated surface sources. In the U.S., the filter question starts from treated water; for a quarter of the world it starts from none.

Lead From Pipes and Plumbing

The most common sources of lead in drinking water are lead pipes, faucets, and fixtures, according to EPA. The agency estimates, with the latest data from 2025, that there are 4 million lead service lines across the country, and lead pipes are more likely to be found in older cities and homes built before 1986.

Homes without a lead line are not automatically clear. Among homes without lead service lines, the most common problem is with brass or chrome-plated brass faucets and plumbing with lead solder. EPA has set the maximum contaminant level goal for lead in drinking water at zero because lead is a toxic metal that can be harmful to human health even at low exposure levels.

Lead and children: EPA and the Centers for Disease Control and Prevention (CDC) agree that there is no known safe level of lead in a child’s blood, and a dose of lead that would have little effect on an adult can have a significant effect on a child. A filter only helps if its certification lists lead.

If your home predates the cutoff, ask your utility whether your service line is lead before choosing any filter. The guide on whether water filter pitchers are necessary covers lead-rated pitchers in more detail.

PFAS Forever Chemicals in Tap Water

USGS estimates at least 45% of the nation’s tap water has one or more types of PFAS, based on tap water samples from 716 locations. The count is conservative: there are more than 12,000 types of PFAS, not all of which can be detected with current tests, and the USGS study tested for the presence of 32 types.

Treatment plants were not built for them. “Most water treatment plants are not set up to remove more modern contaminants, such as PFAS, pharmaceutical drugs and endocrine-disrupting chemicals,” said Detlef Knappe of North Carolina State University. His team found that, on average, pitcher and refrigerator filters that use activated carbon reduced PFAS levels by about 50%, while reverse osmosis systems were over 90% effective, but they are much more expensive and waste a significant amount of water.

Source: NC State Superfund Research Center, 2020 study

The explainer on how a reverse osmosis system works covers the membrane process and the wastewater it produces.

Disinfection Byproducts, Arsenic and Nitrate

EPA’s chemical contaminant rules regulate over 65 contaminants. They target long-term exposure: the rules provide public health protection through the reduction of chronic, or long-term, risks from cancer, organ damage, circulatory system disorders, nervous system disorders, and reproductive system disorders. A filter lowers exposure to what it is certified for, and no filter can promise protection from cancer.

Disinfection is the trade-off behind every tap. Pathogens, such as Giardia, Cryptosporidium, and viruses, are often found in source water and can cause gastrointestinal illness, but disinfectants can react with naturally occurring materials in the water to form byproducts including trihalomethanes (THM), haloacetic acids (HAA), chlorite, and bromate. EPA’s position is measured: byproducts, if consumed in excess of EPA’s standard over many years, may increase health risks.

Arsenic and nitrate show the same pattern. In 2001, EPA adopted a lower standard for arsenic in drinking water, and the new arsenic standard of 10 parts per billion (ppb) replaces the old standard of 50 ppb. Nitrate is the acute exception: there is an acute health risk from nitrate and nitrite, and the regulations reduce the risk of methemoglobinemia or blue baby syndrome.

Private Wells Have No Federal Standard

Around 15% of the U.S. population (over 43 million) rely on private wells as their source of drinking water, according to EPA, and private well owners are responsible for delivering safe drinking water to their households. EPA estimates that more than 23 million households rely on private wells for drinking water in the United States.

CDC advises well owners to test their water at least once each year for harmful germs and chemicals and to consider testing your water if you notice changes in color, taste, or smell.

Key finding: A U.S. Geologic Survey study of 2,100 private wells found that water pumped from about one in five wells contained one or more contaminants at a concentration greater than a human-health benchmark for drinking water. For a well household, the lab test comes before the filter, because the result decides which filter to buy.

Filtered Tap Water Versus Bottled Water

Bottled water carries a plastic load of its own. Columbia University researchers found that, in bottled water, on average, a liter contained some 240,000 detectable plastic fragments, 10 to 100 times greater than previous estimates. By comparison, tap water also has been shown to contain microplastics, though far less than bottled water.

Taste is the other reason people switch, and it is a poor safety test. CDC notes that harmful germs and chemicals often do not change the look, taste, or smell of water, while substances that are not harmful, like some that contain sulfur, can make water taste or smell bad. If taste is the only complaint, a certified taste-and-odor filter on the tap costs less over time than cases of bottled water. The roundup of faucet-mounted water filters compares the tap-side options.

What cannot be filtered out of water?

No single home filter removes everything. According to the CDC, filters cannot remove some types of harmful substances, so you may also consider other water treatment systems. Pore size decides a lot: a filter with an absolute pore size of 1 micron will catch a 1-micron-sized germ, but a filter with a mean pore size of 1 micron may not.

What a filter removes also depends on the size of the filter’s pores, the size of the substance, and the electric charge of the substance. For pitcher and fridge filters, CDC says these filters typically use a carbon filter to make water taste better or remove heavy metals like lead, which leaves germs to a different kind of system.

The Downsides of Drinking Filtered Water

Filters remove both good and bad substances from your water, CDC says, and some filters remove beneficial chemicals like chlorine, which kills germs in water, or fluoride, which prevents cavities. A whole-home unit adds a plumbing risk: if you install a whole-home filter that removes chlorine or other disinfectants, more germs may grow in your plumbing.

Neglect is the other downside. You will need to maintain any filter you use to keep it working properly and prevent germs from growing in it. The guide to buying a water filter pitcher lists cartridge replacement intervals by brand.

How long can water sit in a filter?

Keep filtered water cold and use it quickly. In a lab test of nine different jugs of popular brands sold in the Italian market, refrigeration of the jug containing the filtered water can help significantly delay the development of bacterial flora in water over time. When jugs containing the filtered water were kept at room temperature and the water was not renewed, the highest growth rates for culturable aerobic bacteria could be found.

How to Match a Filter to Your Water

Start with the label, because the certification decides what a filter removes.

Per the CDC, one way to figure out what a water filter removes is to look for an NSF certification on the filter’s label, and the CDC lists these NSF standards related to water treatment:

Source: CDC, About Choosing Home Water Filters, 2024

You can look up specific products in the NSF database to see what they are certified to remove from water, a step the CDC guide to choosing home water filters walks through.

Match the standard to the problem: Read the certification for the specific contaminant named in your water report. A taste-and-odor certification says nothing about lead or PFAS.

What is the safest home water filter?

The safest filter is the one certified for the contaminant in your water, whatever the brand. For PFAS, NC State notes that home filters can now be NSF/ANSI Standard 53 certified for some of those chemicals, while reverse osmosis systems were over 90% effective, but they are much more expensive. Compare installed units in the roundup of reverse osmosis systems for home use, or see how pitcher brands differ in the PUR, Brita, ZeroWater and Mavea comparison.

Conclusion

The reasons to filter drinking water are specific and measurable. EPA counted 6,045 public water systems that violated a health-based drinking water standard in its latest national compliance report; EPA estimates 4 million lead service lines across the country; and USGS estimates at least 45% of the nation’s tap water has one or more types of PFAS. Each figure is a reason to check your own water, and CDC’s point that clean tap water may not need a filter still stands.

Read your utility’s annual report or test your well, match the filter’s NSF certification to what you find, keep filtered water in the fridge, and change the cartridge on schedule. A filter chosen that way solves a real problem; one bought out of fear mostly changes the taste.