Copper

At a glance: Copper in tap water usually comes from copper pipes and fittings inside the home, dissolved by corrosive water. It causes blue-green stains and a metallic taste at lower levels, and stomach upset at higher ones. EPA’s health-based action level is 1.3 mg/L. The lasting fix is to make the water less corrosive or replace the plumbing; for drinking water now, a filter certified for copper at the kitchen tap works.

Stains alone do not tell you whether the water is unsafe. A first-draw test does.

What it is and where it comes from

Copper is a metal widely used in household plumbing. The Minnesota Department of Health says it “can get into your drinking water as the water passes through your household plumbing system,” and that corrosive water dissolves copper from pipes over time. EPA’s health table lists corrosion of household plumbing and erosion of natural deposits as the sources.

Corrosive water is the key. Low pH (acidic) water is the classic cause on private wells, and EPA’s secondary standards list low pH as causing a bitter metallic taste and corrosion. MDH advises flushing water that has sat unused for more than six hours, because standing water picks up more copper.

On city water, utilities must control corrosion under EPA’s Lead and Copper Rule. On private wells, the owner is responsible. EPA’s list of tests for private wells includes pH, lead and copper for homes with older plumbing, and corrosion for wells near mining.

Health and household effects

EPA’s health table describes two kinds of effects:

• Short term: gastrointestinal distress. MDH lists headaches, vomiting, diarrhea, stomach cramps and nausea.
• Long term: liver or kidney damage. MDH adds that long-term exposure can also harm red blood cells.

MDH says infants and people with Wilson’s disease are especially vulnerable. People with Wilson’s disease should talk with their doctor if water tests above the action level.

The household effects come first. EPA’s secondary standard of 1.0 mg/L is set for metallic taste and blue-green staining. MDH lists pinhole leaks, pitting in pipes, and blue-green stains on fixtures as signs of corrosive water, and notes that water high in copper can look blue.

Limits and what they mean

Standard	Level	What it means
EPA health goal (MCLG)	1.3 mg/L	Level with no expected health risk
EPA action level	1.3 mg/L	Utilities must act if more than 10% of tap samples exceed it
EPA secondary standard	1.0 mg/L	Guideline for taste and staining
WHO guideline	2 mg/L	Health-based international guideline

Unlike lead, copper has a health goal above zero. The action level triggers corrosion control by a utility. Private wells are not covered, so compare a well test with these numbers yourself.

How to test

Take a first-draw sample from water that has sat in the pipes for at least six hours, usually first thing in the morning, because that is when copper is highest. Wisconsin’s state lab charges $38 for copper. Penn State’s $85 package adds pH, alkalinity and a corrosivity index, which tell you whether the water itself is the cause.

If copper is high, test lead in the same round, since the same corrosive water attacks lead solder and brass. Our well testing guide covers labs and sampling.

Treatment options

Method	How well it works	Certification to look for	Cost range
Reverse osmosis, point of use	High	NSF/ANSI 58, copper reduction	$300 to $1,500
Carbon filter with a copper claim (activated carbon), point of use	Moderate to high for listed models	NSF/ANSI 53, copper reduction	$10 to $100
Neutralizer for acidic well water (specialty media)	Reduces corrosion at the source	None common	Get a quote
Distillation, point of use	High	NSF/ANSI 62	$300 to $1,200
Flushing and using cold water	Lowers exposure	Not applicable	Free

Cost ranges are Minnesota Department of Health estimates based on 2017 and 2018 quotes, low end self-installed and high end professionally installed.

Wisconsin’s health department lists both carbon filtration certified to NSF/ANSI 53 and reverse osmosis certified to NSF/ANSI 58 for copper. Check that the specific product lists copper, not just the standard number. The filter finder shows each product’s listed claims.

Treat the cause if you can. A point-of-use filter protects what you drink, but corrosive water keeps eating the pipes, which leads to leaks. On a well, fixing low pH protects both your health and your plumbing. Watch for side effects of other treatment too: MDH notes that softening and anion exchange can make water more corrosive.

For how point-of-use and whole-house approaches compare, see whole-house filter vs reverse osmosis.

When to call a professional

Call a water treatment professional if your well water is acidic or tests high for copper, to size a neutralizer or other corrosion control. Retest copper and lead afterward.

Call a licensed plumber if you see pinhole leaks, pitting or blue-green stains, which MDH lists as signs of corrosive water. On city water, call your utility if first-draw copper is above 1.3 mg/L; it is responsible for corrosion control in the water it delivers.