Copper in drinking water: a plain-English guide

Where copper in drinking water comes from

Almost all copper in tap water comes from copper plumbing inside the home: pipes, brass fittings, and water heaters. The amount that leaches depends on water chemistry (corrosive water with low pH or low alkalinity dissolves more copper), how long water has sat in the pipes, and water temperature.

Source water rarely contains meaningful copper. Wells in copper-mineral- rich geology occasionally do, but for the vast majority of U.S. systems, copper at the tap is a plumbing-corrosion story, not a source-water story.

Why it matters for health

Copper is a required dietary nutrient. Adults need about 0.9 mg per day, which is easily met from food. At higher intakes, however, copper causes acute gastrointestinal symptoms: nausea, abdominal cramping, vomiting, and diarrhea, sometimes within hours of drinking water with elevated copper. Chronic exposure at lower levels has been linked to liver damage in rare cases.

Two specific populations are at much higher risk:

• People with Wilson’s disease, a rare genetic disorder of copper metabolism. They cannot excrete copper normally and accumulate it in the liver, brain, and other tissues.
• Infants with biliary atresia and certain other rare hepatic conditions.

Both should drink water tested for copper or use a treatment system known to remove it.

EPA’s regulation

EPA regulates copper under the Lead and Copper Rule, alongside lead:

• Action level: 1.3 mg/L at the 90th percentile of tap samples in a utility’s sampling pool. Exceeding it triggers required corrosion- control treatment.
• MCLG: 1.3 mg/L (same as action level).

The value is set on acute gastrointestinal effects, not on long-term toxicity. There is no separate health-based MCL.

What to do if your tap shows copper

1. Flush before drinking when water has sat in the pipes for hours. The first liter from a tap that hasn’t been used since the night before is the most likely to be high.
2. Use cold water for cooking and drinking. Hot copper-pipe water dissolves more copper.
3. If water tastes metallic or leaves blue-green stains on fixtures, that is a corrosion signal. Contact your utility; the issue may need treatment-plant corrosion control adjustment.
4. Filter at the tap. NSF/ANSI Standard 53 filters with a copper reduction claim are effective. Reverse osmosis works. Standard “chlorine taste” carbon filters generally do not remove copper.

This page is general information, not medical advice. People with Wilson’s disease or specific copper-metabolism concerns should work with their clinician on water sources.

Sources

• US EPA, “National Primary Drinking Water Regulations”: https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations
• US EPA, “Revised Lead and Copper Rule”: https://www.epa.gov/ground-water-and-drinking-water/revised-lead-and-copper-rule
• ATSDR Toxicological Profile for Copper (2022): https://www.atsdr.cdc.gov/toxprofiles/tp132.pdf