EWG's Tap Water Database — 2021 UPDATE

picture of test tube and beaker in laboratory


October 2019


Copper is an essential element in our diet, but too much can cause vomiting, diarrhea, stomach cramps and nausea. It has also been associated with liver damage and kidney disease. The body’s natural mechanisms for maintaining proper levels of copper develop after age 1; as a result, children younger than 1 are more vulnerable to the toxic effects of copper. Water directly from the tap, especially hot water, should not be used to prepare infant formula because hot water leaches more copper from the pipes.

Copper in tap water primarily comes from plumbing pipes. Water utilities are required to sample water in customers’ homes to determine if excessive copper might be a problem. The federal "action level" for copper in drinking water is triggered whenever the level of copper in more than 10 percent of the tap water samples collected by a water system is greater than 1.3 parts per million, or ppm. But this action level is not sufficient to protect susceptible populations, such as infants and people with a rare inherited metabolic disorder known as Wilson’s disease. The state of California set a public health goal for copper at 0.3 ppm to protect infants and children from the gastrointestinal effects of excess copper.

Why is copper in tap water?

Although copper occurs naturally, low levels are typically found in the rivers and lakes that supply drinking water. Copper works its way into tap water by dissolving from copper pipes in household plumbing. Corrosive water conditions, such as acidity or a high concentration of aluminum or chlorine in water, can increase copper leaching.

The longer the water stays in pipes, the more copper will leach into water coming from the faucet. According to the state of Minnesota, homes with new copper pipes are most at risk of leaching. Minerals build up on the inside of pipes over time. Once this coating has developed, water has less contact with the pipe surface and is less likely to pick up copper. To minimize contact, water should be flushed from the tap if it has not been in use for more than six hours.

How is copper in water regulated?

Copper, like lead, is removed with specialized treatment techniques that water utilities use to control the corrosiveness of their water. According to the federal Lead and Copper Rule, 1.3 ppm is the trigger for action. Whenever this action level is exceeded in more than a tenth of samples collected in the water distribution system, utilities must take additional steps to decrease leaching. These steps may include adding a corrosion inhibitor, such as phosphate, or adjusting the water chemistry.

Copper testing at customers’ homes is required for systems serving 50,000 residents or more if tap water samples above action levels indicate additional corrosion control measures are needed. However, the federal action level does not protect infants or people with Wilson’s disease from copper toxicity. California’s public health goal of 0.3 ppm is a guideline aimed to protect infants from diarrhea and vomiting.

What are the health effects of excess copper?

At levels typically detected in U.S. tap water, copper primarily poses a concern for newborn children and infants, as well as for individuals with a genetic copper metabolism disorder.

The copper intake requirement for infants and children is much lower than that for adults. Additionally, infants younger than 1 year old are more susceptible than adults to excess copper, due to their inability to regulate copper. Infants may experience diarrhea, weight loss and even liver cirrhosis if they drink water with too much copper. Infants fed formula reconstituted with tap water are especially at risk of increased copper exposure, because the federal standards are insufficient to protect them.

About 1 percent of Americans have Wilson’s disease, a genetic predisposition to increased copper retention, and are susceptible to copper toxicity that may affect the liver, kidneys and brain, as reported in 2000 by the National Research Council Committee on Copper in Drinking Water.

What to do about copper in your water


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