Chlorate in U.S. tap water

A byproduct that can form during disinfection, especially when hypochlorite solutions degrade. Has no enforceable federal limit but is on the EPA contaminant candidate list; high levels can affect the thyroid.

The federal NL for Chlorate is 800 ug/L. The EPA enforces this against the regulated reporting statistic (typically a running annual average or 90th percentile), not a single-sample spike.

1 of the 55 public water systems on The Water Map report Chlorate at or above its federal limit, spanning 2 U.S. states. The full list is on this page.

Search your city on The Water Map (https://www.thewatermap.com/) or browse the list on this page. Every U.S. public water utility is required to publish an annual Consumer Confidence Report that lists every contaminant it measured, including Chlorate.