Physical & aggregate
Hardness in U.S. tap water
398 public water systems across 25 U.S. states report Hardness in their annual Consumer Confidence Report. None currently sit at or above the federal limit.
What it is
A measure of dissolved calcium and magnesium minerals.
Why it's regulated
Not federally regulated for health; affects scaling, soap use, and taste.
Frequently asked
+What is Hardness?
A measure of dissolved calcium and magnesium minerals. Not federally regulated for health; affects scaling, soap use, and taste.
+Does Hardness have a federal limit in drinking water?
Hardness does not have an enforceable federal MCL. Utilities still report any measured levels in their annual Consumer Confidence Report.
+How many U.S. water systems have Hardness over the federal limit?
Zero of the 398 public water systems in The Water Map dataset currently report Hardness at or above its federal limit.
+How can I check if Hardness is in my city's tap water?
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 Hardness.