Copper in Tap Water: Blue-Green Stains, Health Effects, and the 1.3 mg/L Action Level

Copper in tap water almost always comes from your home’s copper pipes and fittings, not from the river or aquifer your utility draws from. EPA’s trigger for action is 1.3 mg/L: if more than 10% of a water system’s tap samples are above that level, the system has to make its water less corrosive. Short-term exposure to high copper can cause nausea, vomiting and stomach cramps. Long-term exposure above the action level may harm the liver or kidneys. Infants and people with Wilson’s disease are the most sensitive. The simplest protections are free: run the cold tap after water has sat for hours, and never use hot tap water for drinking, cooking or baby formula.

What the 1.3 mg/L action level means

Copper is regulated under EPA’s Lead and Copper Rule, which works differently from most drinking water standards. Instead of a maximum contaminant level that every sample must meet, it uses an action level. Under the current federal rule (40 CFR 141.80), a system exceeds the copper action level when the 90th percentile of its tap samples is greater than 1.3 mg/L. In plain terms, if more than one in ten homes sampled is over 1.3 mg/L, the utility has to act.

EPA’s health goal (MCLG) for copper is also 1.3 mg/L. When the action level is exceeded, the main required response is corrosion control: adjusting the water’s chemistry so it dissolves less metal from pipes.

The 2024 Lead and Copper Rule Improvements lowered the lead action level from 15 to 10 parts per billion, but the copper action level stayed at 1.3 mg/L. The federal rule text says the updated requirements took effect December 30, 2024, and most water systems must comply by November 1, 2027.

Two other numbers sometimes appear on lab reports and in water quality reports:

EPA secondary standard: 1.0 mg/L. This is a non-enforceable guideline for taste and staining. EPA lists copper’s noticeable effects as a metallic taste and blue-green staining.
WHO guideline: 2 mg/L. WHO says this value protects against short-term stomach effects for people whose bodies handle copper normally, and notes copper can stain laundry and fixtures at lower levels.

A utility that meets the action level can still deliver water that picks up copper in your house. The utility’s sampling tells you about the system as a whole. Your own faucet can be higher.

Where copper comes from

The CDC’s Agency for Toxic Substances and Disease Registry (ATSDR) says high copper in drinking water is most likely when a home has copper pipes and acidic water, and is more common in new or recently renovated homes. Minnesota’s health department adds that copper usually enters water from household plumbing, not from groundwater, so private wells are not usually a source of copper on their own.

Three conditions raise the risk:

Corrosive water. Water that is acidic or otherwise aggressive dissolves copper from pipe walls. Some well water and some poorly controlled public supplies fall into this group.
New plumbing. Minnesota notes that copper plumbing less than about three years old usually hasn’t built up the protective coating that limits how much copper dissolves. It also warns that a new private well connected to existing plumbing can change the water chemistry and start dissolving copper.
Standing water. Water that sits in pipes overnight or while you are away picks up more metal. WHO notes that standing or partly flushed water can contain much more copper than water that has been running.

Signs your water may have too much copper

You often can’t see or taste copper at moderate levels, but there are clues:

Blue-green stains on sinks, tubs, toilet bowls or under dripping faucets
A metallic or bitter taste
Water with a light blue or blue-green tint
Pinhole leaks or pitting in copper pipes, which Minnesota lists as signs of corrosive water

None of these confirm a health problem. They are reasons to test.

Health effects

Copper is an essential nutrient. Your body needs it, and Minnesota’s health department notes that most healthy people don’t get sick from copper in water because their bodies regulate it. Problems come with too much, especially over a short period.

Short-term: EPA lists gastrointestinal distress as the main short-term effect. Minnesota’s health department lists nausea, vomiting, diarrhea, stomach cramps and headaches.
Long-term: EPA says long-term exposure above the action level may cause liver or kidney damage.

Who is most sensitive:

Infants. ATSDR’s toxicological profile reports that infants absorb copper more efficiently than adults. Minnesota names infants under one year as a sensitive group and says they may need water with lower copper than 1.3 mg/L. WHO notes formula made with standing tap water can significantly raise a baby’s copper intake.
People with Wilson’s disease, a genetic condition in which the body can’t remove extra copper. EPA advises people with Wilson’s disease to talk to their doctor if their water is above the action level.

If you think someone has been exposed to high copper levels, ATSDR’s advice is to talk to a doctor, nurse or clinic, or call poison control. If you’re preparing formula or someone in your home has a health condition, ask your doctor what level is appropriate.

Flushing: the free fix

Because most copper comes from water sitting in your own pipes, flushing works well:

If water hasn’t been used for more than six hours, run the cold tap for 30 to 60 seconds before drinking or cooking. This is Minnesota Department of Health guidance.
Use cold water only for drinking, cooking and baby formula. Hot water releases more copper from pipes.

If you also suspect lead in your plumbing, the same habits help. Our guide to lead in tap water covers the extra steps that apply to lead.

How to test

Your utility’s annual water quality report lists its copper results as a 90th percentile value and the number of sites above the action level. That tells you how the system is doing, not what comes out of your tap.

To know your own level, use a state-certified lab. Ask whether the lab wants a first-draw sample (water that sat overnight) and a flushed sample. Comparing the two shows whether copper is coming from your plumbing and whether flushing brings it down. Minnesota recommends testing especially when an infant or someone with Wilson’s disease drinks the water.

Treatment options

If your flushed water is still above 1.3 mg/L, or a sensitive person drinks it, consider a home treatment device. NSF International certifies filters for copper reduction under two standards:

NSF/ANSI 53 (carbon and other filters with a copper claim). NSF says these are tested with water containing 3 mg/L copper and must bring it below 1.3 mg/L.
NSF/ANSI 58 (reverse osmosis). NSF says certified RO systems reduce copper below the action level.

“NSF certified” on a box is not enough. The product has to be listed for copper reduction specifically. Search the NSF certified product listings by contaminant and confirm the exact model before you buy. See reverse osmosis vs. carbon filters for the trade-offs.

For private well owners with corrosive water, filters at the tap treat the symptom. Correcting the water chemistry (for example, with a neutralizing system for acidic water) addresses the cause. A water treatment professional or your county health office can help you decide.

What to do if your city’s water is over the action level

If your utility reports a copper action level exceedance, it is required to study and adjust corrosion control. In the meantime, flush, use cold water, and consider testing your own tap. You can look up your system’s record on its page through our ZIP code search. Grades there reflect public EPA data as described in our methodology.

Bottom line

Copper is mostly a plumbing problem, not a source-water problem. Blue-green stains and a metallic taste are the classic signs. EPA’s action level is 1.3 mg/L, and the people who need the most care are babies and anyone with Wilson’s disease. Flush standing water, use only cold water for drinking and formula, test your own tap if you have new copper plumbing or a sensitive household member, and choose a filter that is listed specifically for copper reduction if you need one.