Physical & aggregate
Hardness in U.S. tap water
124 public water systems across 26 U.S. states report Hardness in their annual Consumer Confidence Report. 4 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.
At or above the federal limit (4)
| Water system | Measured | vs. limit |
|---|---|---|
| Pomona, CA 2024 annual report | 241–272 mg/L | 272.0× the limit |
| Burbank, CA 2024 annual report | 148–300 mg/L | 100.0× the limit |
| San Diego, CA 2023 annual report | 13.4 | 22.3× the limit |
| Vancouver, WA 2024 annual report | 140 mg/L | 1.0× the limit |
Within the federal limit (4)
| Water system | Measured |
|---|---|
| Elizabeth, NJ 2024 annual report | 143 mg/L |
| Lakewood, NJ 2025 annual report | 140 mg/L |
| Overland Park, KS 2023 annual report | 137 |
| Salem, OR 2023 annual report | 16 mg/L |
Frequently asked
+What is Hardness?
A measure of dissolved calcium and magnesium minerals. Not federally regulated for health; affects scaling, soap use, and taste.
+What is the federal limit for Hardness in drinking water?
The federal MCL for Hardness is 3 mg/L. The EPA enforces this against the regulated reporting statistic (typically a running annual average or 90th percentile), not a single-sample spike.
+How many U.S. water systems have Hardness over the federal limit?
4 of the 124 public water systems on The Water Map report Hardness at or above its federal limit, spanning 26 U.S. states. The full list is on this page.
+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.