Tap water in the United States is generally safe to drink, but “safe” doesn’t mean free of contaminants. Municipal water can contain lead from old pipes, byproducts from the disinfection process, agricultural chemicals, and synthetic compounds that weren’t regulated until recently. Whether your tap water is actually a problem depends on where you live, how old your plumbing is, and what’s happening between the treatment plant and your faucet.
Lead Leaches From Old Pipes
The EPA has set its safety goal for lead in drinking water at zero, because lead is toxic at any level. Yet millions of homes in the U.S. still connect to water mains through lead service lines, and these pipes are the single largest source of lead in tap water. Lead enters the water through corrosion, a chemical reaction between the water and the metal. Several factors speed this up: acidic water, hot water, and water that sits in pipes for long periods.
The consequences are most serious for children. Even low blood lead levels in kids are linked to learning disabilities, lower IQ, hyperactivity, slowed growth, and hearing problems. In adults, lead exposure raises blood pressure, damages kidneys, and causes reproductive issues in both men and women. Water systems are required to act when more than 10 percent of samples exceed 15 parts per billion, but the EPA is clear that no amount is truly safe.
If your home was built before the mid-1980s, there’s a higher chance your plumbing contains lead solder or lead service lines. Running cold water for 30 seconds to two minutes before drinking (to flush standing water from the pipes) reduces exposure. Using a filter certified to remove lead is more reliable.
Chlorine Disinfection Creates Byproducts
Chlorine kills dangerous bacteria in water, and it’s one of the most important public health tools of the last century. The tradeoff is that chlorine reacts with organic matter naturally present in source water to form compounds called disinfection byproducts. The most studied of these are trihalomethanes (THMs).
A 2025 systematic review pooling data from thousands of cancer cases found that people with the highest THM exposure had a 33 percent increased risk of bladder cancer compared to those with the lowest exposure. Colorectal cancer risk was 15 percent higher. The dose-response analysis showed the bladder cancer risk became statistically significant above THM concentrations of 41 micrograms per liter, which is below the current regulatory limit in both the U.S. and the EU. In other words, the legal ceiling may not fully protect against cancer risk at the population level.
You can reduce your exposure by using an activated carbon filter (the kind found in common pitcher filters), which removes most THMs effectively.
PFAS: The “Forever Chemicals”
PFAS are a family of thousands of synthetic chemicals used in nonstick coatings, food packaging, firefighting foam, and waterproof fabrics. They’re called “forever chemicals” because they don’t break down in the environment. They’ve been detected in the drinking water of communities across the country.
In April 2024, the EPA finalized the first-ever national limits for PFAS in drinking water, setting the maximum contaminant level for the two most studied compounds, PFOA and PFOS, at 4.0 parts per trillion. The health goal was set at zero. Water systems have until 2029 to comply, so widespread testing and treatment is still ramping up. PFAS exposure has been associated with immune system effects, certain cancers, thyroid disruption, and reproductive harm.
Nitrates From Agricultural Runoff
In farming regions, fertilizer and animal waste wash nitrogen compounds into groundwater and surface water. The legal limit for nitrate in U.S. drinking water is 10 milligrams per liter, a number set decades ago specifically to prevent a condition in infants called methemoglobinemia, or “blue baby syndrome.” In this condition, nitrite (which forms from nitrate) binds to hemoglobin and blocks the blood from carrying oxygen. In severe cases it’s life-threatening.
That legal limit was designed only to prevent methemoglobinemia. It did not account for other health concerns that have since emerged in the research, including possible links to cancer and adverse reproductive outcomes. If you live in an agricultural area and your water comes from a well or a small system drawing from groundwater, nitrate is worth testing for.
What Happens Between the Plant and Your Faucet
Even when water leaves a treatment plant in good condition, it can degrade on the way to your tap. The U.S. has roughly a million miles of water mains, much of it decades old. As metallic pipes corrode internally, they develop rough, pitted surfaces where bacteria colonize and form biofilms. These biofilms are slimy layers of microorganisms that can shelter pathogens from disinfectants, cause taste and odor problems, and actually increase the formation of disinfection byproducts.
Sediment that accumulates in aging pipes can also serve as a nutrient source for bacteria. The longer water sits in the system before reaching your tap (a factor engineers call “water age”), the more time corrosion, biofilm growth, and chemical reactions have to alter its quality. Homes at the end of long distribution lines, or in areas with low water usage, tend to have older water and potentially more degradation.
Private Wells Have No Federal Oversight
If your water comes from a private well, it falls outside the Safe Drinking Water Act entirely. The federal government does not regulate private well water quality, and most state governments don’t either. You are solely responsible for testing and treating your own supply.
A U.S. Geological Survey study of 2,100 private wells found that about one in five contained at least one contaminant above a human health benchmark. Common culprits include bacteria, nitrates, arsenic, radon, and heavy metals. Without regular testing, well owners often have no idea what’s in their water. Annual testing for bacteria and nitrates is a reasonable minimum, with additional tests for arsenic, lead, or pesticides depending on local geology and land use.
Microplastics Are Present but Poorly Understood
Tiny plastic fragments have been found in tap water samples worldwide. Concentrations vary enormously depending on how they’re measured and what particle size researchers look for. Studies examining particles larger than 100 micrometers have found averages around 10 particles per liter, while those counting much smaller fragments report hundreds or even thousands per liter. One review of 21 studies confirmed microplastics are present in both tap and bottled water, with concentrations increasing sharply as particle size decreases. Bottled water actually tends to contain more microplastics than tap water.
The health effects of ingesting these particles over a lifetime are still unclear. Concerns center on the plastic polymers themselves, chemical additives within them, and other pollutants or microorganisms that cling to their surfaces. No regulatory limits exist for microplastics in drinking water.
Unregulated Contaminants
The EPA regulates roughly 90 contaminants in drinking water. But thousands of chemicals are used in industry, agriculture, and consumer products, and many that show up in water supplies have no enforceable federal limit. The EPA maintains a Contaminant Candidate List of substances known or expected to appear in public water systems that may eventually need regulation, but the process of studying, proposing, and finalizing a new standard takes years to decades. PFAS is a recent example: the chemicals were in widespread use for over 50 years before enforceable limits were set in 2024.
What You Can Actually Do
Your water utility is required to publish an annual Consumer Confidence Report listing detected contaminants and their levels. Reading yours is the single best starting point for understanding what’s in your specific water. You can usually find it on your utility’s website or request a copy.
If you’re on a private well, testing is your responsibility and should happen at least annually. For municipal water, a home filter can address most of the concerns above, but the type matters. Activated carbon pitchers and faucet filters handle chlorine, THMs, and some lead. Reverse osmosis systems remove a broader range of contaminants including PFAS, nitrates, and lead. No single filter removes everything, so match your filter to the specific contaminants in your water report.
Running your tap for 30 seconds before filling a glass flushes out water that’s been sitting in contact with your home’s plumbing. Using cold water for drinking and cooking matters too, since hot water dissolves more lead and other metals from pipes. These are simple habits, but for homes with older plumbing, they make a measurable difference.