Water Quality by City
Explore tap water quality for 201+ major US cities. See water sources, common contaminants, and get a free water quality report for your ZIP code.
Why water quality varies from city to city
Two cities in the same state can have dramatically different tap water quality. The reasons come down to three main factors: where the water comes from, how it is treated, and how it reaches your tap.
Water source is the biggest variable. Cities drawing from protected mountain reservoirs or deep aquifers generally start with cleaner water than those pulling from rivers that carry agricultural and industrial runoff. For example, New York City and Portland, Oregon both benefit from pristine mountain watersheds, while cities along the Ohio or Mississippi Rivers must treat water carrying upstream pollution.
Treatment technology matters too. Some cities have invested billions in advanced treatment, including granular activated carbon, ozone disinfection, and reverse osmosis. Others, particularly smaller or financially stressed systems, may rely on more basic treatment that meets minimum standards but does not remove all contaminants of concern.
Finally, the distribution system between the treatment plant and your faucet can introduce contaminants. Lead service lines, corroding iron mains, and cross-connections can all affect water quality at the tap, even when the treated water leaving the plant is clean. Cities with older infrastructure face the greatest challenges in this area.
Check your specific water
City-level information provides useful context, but the best way to know what is in your tap water is to look up your ZIP code for a report based on your specific water system. Water quality can vary between neighborhoods served by different water systems or distribution mains.
Know your water
Enter your ZIP code for a free water quality report specific to your address.