Check my ZIP: what to test, local risks, nearest certified labs

Your county. We match your ZIP to its Census ZIP Code Tabulation Area (ZCTA). The county shown first holds the largest land part of that area; a ZIP that crosses county lines also lists the others. PO-box-only and single-business ZIPs have no Census area, so they are not found: use the ZIP of your street address.

County facts. The private-well population is the USGS 2015 estimate of people on domestic self-supplied water. The arsenic figure is a USGS model estimate of private-well users with arsenic above 10 µg/L, EPA's limit for public water, on a 2010 population base; USGS describes this kind of estimate as useful "for broad screening of the population at risk", so it says nothing certain about any one well. EPA's radon zones describe radon in indoor air, and EPA says the map should not be used to decide whether an individual home needs testing.

Distances. Miles are straight-line distances from the middle of your ZIP area (the Census internal point) to the lab, not driving distance. In very large rural ZIP areas, as in parts of Alaska and the West, that point can be many miles from your home. Most labs are placed by their street address; 2,193 of 2,291 labs on our lists have a map point, and labs placed only by their ZIP are marked "location approximate (ZIP)". A state's list can include labs in other states, often used as mail-in labs, so the nearest lab may be across a state line. Before you send a sample, call the lab to confirm it is certified for the exact test and takes samples from homeowners. Bacteria samples have short holding times, so ask about delivery before you mail one.

What to test. The tool repeats what EPA, your state and the county data say. It is context for your area, not a diagnosis of your water: only a test tells you what is in your well. For tests that depend on your home, use the which-tests checklist; when results arrive, check your numbers against EPA's limits.