Copper in drinking water: stains, limits & what to do.
Copper reaches tap water almost entirely by corroding household copper pipe and brass fittings — rarely from the source. It is regulated by a treatment-technique action level of 1.3 mg/L at the 90th percentile of tap samples (its MCLG is the same), not a normal MCL. The visible clue is blue-green staining; the fix is corrosion control plus flushing standing water.
Copper is regulated by an action level — not a normal MCL.
Copper and lead share one rule — the federal Lead and Copper Rule. This page is the household-and-small-system answer; for the clause-by-clause rule reference, see our Lead and Copper Rule (LCR / LCRI) page.
An exceedance is not an automatic violation — it is a trigger that puts the system on corrosion control and a set of notices.
- 1 · 90th-percentile tap copper > 1.3 mg/L (more than 10% of samples over)
- 2 · Treatment-technique trigger not an MCL violation
- 3 · Corrosion control + consumer notice of tap results within 3 business days — §§ 141.81 · 141.85(d)
Source: 40 CFR §§ 141.80(c) · 141.51 · 141.85 · 143.3
What to do about copper at home
Flush the standing water
Copper dissolves into water that has sat in your pipes overnight or over a weekend. Run the cold tap for 30 to 60 seconds — until it turns noticeably colder — before you drink, cook, or mix infant formula. The flushed water is fine for plants or cleaning (EPA, Lead and Copper Rule).
Use cold water, never hot
Hot water dissolves copper from plumbing far faster than cold, and boiling does not remove copper — it concentrates it as water evaporates. Draw cold water for anything you drink or cook, and heat it on the stove if you need it warm.
The blue-green stain is the clue
Blue-green staining on sinks, tubs, and toilets, plus a metallic or bitter taste in cold morning water, is the visible sign of copper leaching from your own pipes. That aesthetic threshold is the 1.0 mg/L secondary standard (40 CFR § 143.3). If you see it, collect a first-draw sample for a certified lab.
Corrosion control is the system's job
Because copper comes from your plumbing, the fix is making the water less corrosive — the water system's responsibility under the Lead and Copper Rule (40 CFR § 141.81). Ask whether your system has optimized corrosion control. Meanwhile, a filter certified to NSF/ANSI 53 for copper reduction lowers it at the kitchen tap.
Where copper in drinking water comes from
Your household plumbing
Copper is rarely in the water that leaves the treatment plant. EPA lists the primary source as "corrosion of household plumbing systems" — copper pipe, brass fittings, and fixtures that dissolve into the water sitting against them (EPA, National Primary Drinking Water Regulations).
Corrosive water
Low-pH, low-alkalinity, low-mineral (soft) water is aggressive — it dissolves copper from pipe walls. The more corrosive the water, the more copper it picks up, which is why corrosion control treatment targets pH and alkalinity rather than the source.
Rarely the natural source
EPA also names "erosion of natural deposits" as a minor source, but source-water copper is usually low. This is what makes copper a plumbing-and-corrosion problem rather than a treat-at-the-plant one — for most systems it is fixed at the pipe, not the well.
What copper exposure does — short term and long term
EPA’s mandatory health-effects language for copper, reproduced verbatim (40 CFR Part 141, Subpart O, Appendix A):
“Copper is an essential nutrient, but some people who drink water containing copper in excess of the action level over a relatively short amount of time could experience gastrointestinal distress. Some people who drink water containing copper in excess of the action level over many years could suffer liver or kidney damage. People with Wilson's disease should consult their personal doctor.”
Short-term: gastrointestinal distress
Drinking water above the action level over a short time can cause nausea, vomiting, stomach cramps, or diarrhea within hours — the effects the 1.3 mg/L threshold is set to prevent. The most sensitive people in a household notice it first, and symptoms ease once the exposure stops (EPA, National Primary Drinking Water Regulations).
Long-term: liver or kidney damage
Sustained exposure to copper above the action level over many years can lead to liver or kidney damage (EPA). Most healthy adults can drink water at the action level for years without a measurable effect — the standard is set to protect the most sensitive, not the average adult.
Wilson's disease and infants
People with Wilson's disease — a rare inherited disorder that stops the body from clearing copper — should consult their doctor if copper exceeds the action level (EPA). Infants under one year regulate copper less well, so they are also among the sensitive groups.
An essential nutrient at low levels
Copper is a required trace nutrient — the concern is excess, not its presence. EPA sets the MCLG (health goal) at 1.3 mg/L, the level below which no known or anticipated health effects occur with a margin of safety (40 CFR § 141.51). That is why the goal and the action level are the same number.
A copper exceedance is a treatment-technique trigger — not an MCL violation.
Copper is regulated by a treatment technique, so exceeding the 1.3 mg/L action level at the 90th percentile (40 CFR § 141.80(c)) does not, by itself, create an MCL violation or a public notice. It obligates you to install or re-optimize corrosion control (§ 141.81) and monitor water-quality parameters, while every sampled household separately receives its individual tap result within three business days (§ 141.85(d)) as a standing duty. Mass public education is triggered by a lead exceedance, not copper. The full clause map is on our Lead and Copper Rule reference.
1water’s CCR agent reports your 90th-percentile copper result each year, and the compliance validator checks it against the § 141.80(c) action level. Sampling-schedule and consumer-notice tooling for the Lead and Copper Rule is rolling out — so the 90th percentile is computed with an audit trail, not by hand. Tell us your state →
Copper in drinking water — common questions
- U.S. EPA — Lead and Copper Rule, copper action level 1.3 mg/L and 90th-percentile calculation, 40 CFR § 141.80(c); corrosion control treatment, § 141.81; consumer notice of tap results, § 141.85(d).
- U.S. EPA — maximum contaminant level goals, copper MCLG 1.3 mg/L, 40 CFR § 141.51; EPA mandatory health-effects language for copper, 40 CFR Part 141 Subpart O Appendix A.
- U.S. EPA — National Secondary Drinking Water Regulations, copper secondary maximum contaminant level 1.0 mg/L (non-enforceable, aesthetic), 40 CFR § 143.3.
- U.S. EPA — National Primary Drinking Water Regulations table: copper health effects (gastrointestinal distress; liver or kidney damage) and source (corrosion of household plumbing systems; erosion of natural deposits).
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