Is Your Tap Water Safe to Drink?

The EPA regulates over 90 contaminants in public drinking water, but thousands of additional chemicals have been detected in water supplies that are not yet subject to federal limits. Understanding the most common contaminants and their health effects is essential for making informed decisions about your drinking water and whether you need a filter.

Lead is one of the most dangerous drinking water contaminants because there is no safe level of exposure, particularly for children. Lead exposure causes irreversible brain damage in developing children, reduces IQ, and is linked to behavioral problems, kidney damage, and cardiovascular disease in adults. Lead typically enters water through aging infrastructure: lead service lines connecting homes to water mains, lead solder used in copper pipe joints before 1986, and older brass fixtures. Even cities with excellent source water can have lead problems at the tap if homes and service lines have not been updated.

PFAS (per- and polyfluoroalkyl substances), commonly called "forever chemicals," are a class of over 12,000 synthetic chemicals that do not break down in the environment or the human body. They accumulate over time and are linked to multiple cancers, thyroid disease, immune system suppression, reproductive harm, and liver damage. PFAS entered water supplies through firefighting foam used at military bases and airports, industrial manufacturing, and everyday consumer products like non-stick cookware and stain-resistant fabrics. The EPA established new enforceable limits in 2024 for six PFAS compounds, setting maximum levels of 4 parts per trillion for PFOA and PFOS, two of the most studied and harmful compounds in the group.

Disinfection byproducts (DBPs) are chemical compounds that form when chlorine or other disinfectants react with natural organic matter in water during the treatment process. The most common DBPs are trihalomethanes (THMs) and haloacetic acids (HAA5), both of which are linked to increased cancer risk with long-term exposure, as well as reproductive and developmental problems. DBPs are particularly common in cities that rely on surface water sources like rivers and reservoirs, which contain more organic material than groundwater. While disinfection is essential for killing harmful bacteria, the byproducts it creates represent a trade-off that can be addressed through improved treatment methods or home filtration with activated carbon.

Arsenic is a naturally occurring element found in rock and soil that dissolves into groundwater, making it most prevalent in regions that rely on well water and aquifers, particularly in the Southwest and parts of New England. Long-term arsenic exposure at levels above the EPA limit of 10 parts per billion is associated with skin, bladder, and lung cancer, as well as cardiovascular disease and diabetes. The EWG recommends a much lower threshold of 0.004 ppb based on a one-in-a-million cancer risk standard. Reverse osmosis filters are the most effective method for removing arsenic from drinking water at the household level.