Tap water in the United States is among the most regulated in the world, but that doesn’t mean every glass is free of problems. In 2020, about 4% of public water systems in the U.S., roughly 6,481 systems, violated a health-based drinking water standard. The issues range from invisible chemical contamination to aging pipes that quietly degrade water quality between the treatment plant and your faucet. Whether your water looks, smells, or tastes off, or you’re concerned about contaminants you can’t detect, here’s what could actually be wrong and what you can do about it.
Signs Your Water Has a Problem
Some water issues announce themselves. Cloudy or frothy water can indicate suspended particles, detergents, or elevated metal concentrations. A yellowish or brownish tint often points to iron or manganese, typically from corroding pipes. A rotten-egg smell suggests hydrogen sulfide, while a turpentine-like odor may signal contamination by organic chemical compounds. A strong chlorine taste or smell, while not necessarily dangerous, means disinfectant levels are on the higher end of what your utility uses to kill bacteria.
The trickier problems are the ones you can’t see, smell, or taste at all. Lead, PFAS (sometimes called “forever chemicals”), nitrates, and many bacteria produce no obvious changes in your water. That’s why sensory clues are helpful starting points but never the full picture.
Lead and Aging Pipes
Much of the country’s water infrastructure is decades old, and deteriorating pipes are one of the biggest sources of contamination. When metal pipes corrode, they can leach lead, copper, and iron directly into the water flowing through them. Corrosion also creates physical breaches, tiny cracks and leaks, that allow bacteria, viruses, and soil contaminants to seep in from the surrounding ground.
Lead is the most concerning pipe-related contaminant. In children, even low levels of lead exposure have been linked to learning disabilities, lower IQ, hyperactivity, slowed growth, hearing problems, and anemia. In rare cases, lead ingestion can cause seizures, coma, or death. Adults face a different set of risks: increased blood pressure, decreased kidney function, and reproductive problems in both men and women. Lead pipes, lead solder, and brass fixtures are all potential sources, and the water leaving your treatment plant can be perfectly clean yet pick up lead on the way to your tap.
Corrosion does more than release metals. It creates rough surfaces inside pipes where bacteria colonize in layers called biofilms. These biofilms can harbor organisms like Legionella, which causes a severe form of pneumonia. Corroded pipe surfaces also consume the disinfectant residual that’s supposed to protect water during its journey through the system, leaving it more vulnerable to contamination the farther it travels from the treatment plant.
PFAS: The “Forever Chemicals”
PFAS are a family of synthetic chemicals used in nonstick cookware, water-resistant clothing, firefighting foam, and food packaging. They earned the nickname “forever chemicals” because they don’t break down naturally in the environment or in your body. They’ve been detected in drinking water supplies across the country.
In 2024, the EPA finalized the first-ever enforceable limits for PFAS in drinking water. The maximum contaminant levels are set at 4.0 parts per trillion for PFOA and PFOS, the two most studied PFAS compounds, and 10 parts per trillion for three others (PFHxS, PFNA, and GenX chemicals). To put “parts per trillion” in perspective, that’s roughly equivalent to a single drop of water in 20 Olympic-sized swimming pools. The standards are strict because even very small exposures over time have been associated with health effects including certain cancers, thyroid problems, and immune system suppression.
Microplastics in Tap and Bottled Water
Tiny plastic fragments have been found in both tap water and bottled water worldwide. In tap water, studies have detected anywhere from a handful of particles per liter to over 400 particles per liter, depending on the size of particles measured and the location sampled. The smaller the particle size researchers look for, the more they find. One study measuring particles between 1 and 10 micrometers (far smaller than the width of a human hair) found an average of 266 particles per liter in tap water.
Bottled water isn’t a cleaner alternative. Research consistently finds higher microplastic concentrations in bottled water than in tap water, likely because plastic bottles themselves shed particles into the liquid. Studies of PET bottles have found concentrations ranging from around 300 particles per liter up to thousands per liter for the smallest particle sizes. The long-term health effects of ingesting microplastics are still being studied, but the presence of these particles in virtually all drinking water sources is a growing concern.
Bacteria, Viruses, and Parasites
Municipal water treatment is designed to kill pathogens, but breakdowns happen. The CDC lists 11 germs that can contaminate tap water systems, including Cryptosporidium, Giardia, E. coli O157, Legionella, norovirus, Salmonella, hepatitis A virus, and Campylobacter. Most of these cause gastrointestinal illness with symptoms like diarrhea, vomiting, and stomach cramps. Legionella is different: it causes respiratory illness when contaminated water is inhaled as mist, such as from a shower or cooling tower.
Contamination by these organisms typically happens when the physical integrity of the water system breaks down. Three conditions have to occur simultaneously for outside contaminants to enter the system: low or negative pressure in the pipes, a physical gap like a crack or break, and the presence of pathogens in the surrounding soil or groundwater. Aging infrastructure makes the first two conditions increasingly common.
Private Wells Have Different Risks
If your water comes from a private well, it’s not regulated by the EPA or monitored by any utility. You’re responsible for testing and treatment. The CDC recommends testing your well at least once every year for total coliform bacteria, nitrates, total dissolved solids, and pH levels. Depending on your area, you may also need to test for pesticides, heavy metals, or volatile organic compounds. Nitrate contamination is particularly common in agricultural areas and is dangerous for infants, potentially causing a condition that reduces the blood’s ability to carry oxygen.
How to Test Your Water
If you’re on a public water system, your utility is required to publish an annual Consumer Confidence Report listing detected contaminants and whether they meet federal standards. That report covers what leaves the treatment plant, though, not necessarily what arrives at your faucet after traveling through your neighborhood’s pipes and your home’s plumbing.
For a more complete picture, you can send a sample to a state-certified drinking water laboratory. The EPA maintains a directory of certified labs organized by state. Basic tests for bacteria and common metals typically cost between $20 and $100, while comprehensive panels that include PFAS or pesticides can run several hundred dollars. If you’re on a private well, this kind of independent testing is the only way to know what’s in your water.
Filtration Options That Work
No single filter removes everything, so the right choice depends on what’s in your water. Granular activated carbon (GAC) filters, the technology behind many countertop and under-sink systems, are effective at removing chlorine taste and odor, many organic compounds, and a significant portion of PFAS. EPA research estimates that GAC filtration can cost-effectively treat 76 to 87% of PFAS chemicals studied.
Reverse osmosis systems force water through a membrane with extremely fine pores, removing lead, PFAS, nitrates, fluoride, and most dissolved contaminants. They’re among the most thorough options for home use but produce wastewater and are typically installed under the sink for drinking water only. UV disinfection systems kill bacteria and viruses using ultraviolet light but don’t remove chemical contaminants, so they’re best paired with another filter type. Simple pitcher filters using activated carbon can reduce chlorine and improve taste but generally aren’t rated for lead or PFAS removal unless specifically certified for those contaminants.
Look for filters certified by NSF International to the specific standard that matches your concern: NSF/ANSI 53 for lead, NSF/ANSI 58 for reverse osmosis contaminant reduction, and NSF/ANSI P473 for PFAS. The certification means the filter has been independently tested and verified to remove what it claims.