Live national data · EPA UCMR5
PFAS were detected at 3,539 public water systems EPA tested — 1,717 exceed the new EPA limit.
See PFAS occurrence & the most-affected systems →PFAS (“forever chemicals”)
Per- and polyfluoroalkyl substances. EPA set the first enforceable national limits in 2024.
EPA limit · 4 ppt (PFOA & PFOS)
Lead
Rarely in the source water — it usually enters at the tap from old service lines and plumbing.
EPA limit · 15 ppb (action level)
Total trihalomethanes (TTHMs)
A byproduct formed when chlorine disinfectant reacts with natural organic matter in water.
EPA limit · 80 ppb (MCL)
Nitrate
Mostly from agricultural runoff and septic systems; an acute risk to young infants.
EPA limit · 10 ppm (MCL)
Arsenic
A naturally occurring element; long-term exposure raises cancer and cardiovascular risk.
EPA limit · 10 ppb (MCL)
Chromium-6 (hexavalent chromium)
The “Erin Brockovich” chemical. EPA regulates total chromium; California sets a separate Cr-6 limit.
EPA limit · 100 ppb (total chromium)