Copper in drinking water usually comes not from the original water source, but from household plumbing. The Minnesota Department of Health says copper can leach into water as it moves through copper pipes, fittings, or other plumbing components, especially when water sits in the pipes for long periods or when the plumbing is relatively new and has not yet developed a protective mineral coating.
The page explains that copper is an essential nutrient in small amounts, but too much can be harmful. High copper exposure from drinking water may cause headaches, nausea, vomiting, diarrhea, stomach cramps, liver damage, kidney disease, and red blood cell problems. It also notes that infants under one year old and people with Wilson’s disease are more sensitive because their bodies do not remove excess copper as effectively.
Minnesota’s guidance says drinking water with more than 1,300 micrograms of copper per liter can present a health risk. To reduce exposure, the state recommends letting the water run for 30 to 60 seconds before using it for drinking or cooking if it has been sitting in the pipes for more than six hours, and using only cold water for drinking, cooking, and making infant formula because hot water can dissolve more copper from plumbing.
The department also recommends testing tap water if there is ongoing concern, especially if an infant or someone with Wilson’s disease may drink it. If testing still shows copper above 1,300 µg/L after flushing the tap, the page says homeowners may want to consider home water treatment. For private well users, the page notes that copper usually does not come from the groundwater itself, but from plumbing materials in the home.
For people on public water systems, the page explains that the U.S. EPA uses an action level of 1,300 µg/L. Public water systems must act if more than 10% of tested homes and sampling sites exceed that level. However, the page cautions that a home’s own plumbing may still produce higher copper levels at the tap than what appears in the community system’s general water quality report.
The page also notes that signs of corrosive water can include pinhole leaks, pitting in pipes, blue-green staining on fixtures, or water that tastes bad, smells unusual, or appears blue. It adds that if corrosive water is present, lead may also be a concern. The Minnesota Department of Health last updated the page on September 25, 2024.
