Copper in Drinking Water

Copper in tap water most often comes from the corrosion of household plumbing — pipes, fittings, and fixtures — not from the source water itself. Federal regulations address copper under the same framework as lead: a treatment technique requirement built around an action level, not a Maximum Contaminant Level.

How copper gets into drinking water

Copper enters drinking water primarily through the dissolution of copper pipes and brass or bronze fittings inside buildings. The process is called leaching, and it accelerates when water is corrosive — meaning low pH, low alkalinity, or high dissolved oxygen. Utilities have no direct control over the plumbing inside customers' homes, which is why the regulatory model focuses on what utilities can do at the system level: adjust water chemistry to reduce corrosiveness.

Natural geological deposits can also release trace amounts of copper into source water, but household plumbing corrosion is the dominant pathway for tap-water exposure in systems that have copper distribution infrastructure.

The distinction matters for the Consumer Confidence Report. Appendix A to Subpart O of 40 CFR Part 141 lists the major sources in drinking water as: "Corrosion of household plumbing systems; Erosion of natural deposits." Both must be disclosed. (40 CFR Appendix A to Subpart O of Part 141)

Health effects

At normal concentrations, copper is an essential nutrient. At elevated concentrations — specifically, at levels above the action level of 1.3 mg/L — copper poses two distinct health concerns.

Federal regulation at 40 CFR Part 141, Appendix A to Subpart O specifies the exact health-effects language utilities must use in the CCR when an action-level exceedance occurs. The verbatim boilerplate reads:

"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."

(40 CFR Appendix A to Subpart O of Part 141)

This boilerplate is mandatory — utilities cannot substitute different language — and it triggers only when the system's 90th percentile tap sample result exceeds 1.3 mg/L. When no exceedance occurs, utilities still disclose copper monitoring results in the CCR's regulated contaminants table, but the boilerplate language does not apply.

People with Wilson's disease, a genetic disorder that impairs copper metabolism, face heightened risk at any elevated exposure level and are specifically named in the required language.

How copper is regulated: AL not MCL

Copper is regulated as a treatment technique under 40 CFR Part 141 Subpart I (§§ 141.80–141.91), the same subpart that governs lead. (Cornell LII, 40 CFR Part 141 Subpart I)

This matters for how the CCR table is structured. Most contaminants in a CCR have a Maximum Contaminant Level — a hard numerical limit whose violation triggers mandatory public notice. Copper works differently. There is no MCL violation for copper. Instead, exceeding the action level of 1.3 mg/L triggers a required set of follow-on actions: optimized corrosion control treatment, public education, and in some cases, lead service line replacement steps. The violation, if any, is a failure to take those required actions — not the copper measurement itself.

The statutory chain runs from the Safe Drinking Water Act (Pub. L. 104-182, 1996) through the America's Water Infrastructure Act (AWIA, Pub. L. 115-270, 2018) to the Lead and Copper Rule (LCR, 1991), Lead and Copper Rule Revisions (LCRR, 2021), and Lead and Copper Rule Improvements (LCRI, October 2024). (EPA, Lead and Copper Rule Improvements)

What 1.3 mg/L means and how it's measured

The copper action level is 1.3 mg/L (milligrams per liter, equivalent to parts per million). This number has remained unchanged across the LCR, LCRR, and LCRI. (40 CFR § 141.80)

The MCLG for copper is also 1.3 mg/L — meaning EPA set the health-protective goal at the same level as the action level. This is unusual. For lead, the MCLG is zero (no safe level). For copper, the agency determined that 1.3 mg/L represents a level below which health risk is negligible for the general population, so the action level and the health goal coincide.

Measurement uses tap sampling at high-risk sites — locations within the distribution system most likely to have elevated copper due to corrosive plumbing. Utilities collect a specified number of samples, then identify the 90th percentile result. If that 90th percentile result exceeds 1.3 mg/L, the action level is exceeded and the system must respond.

The sampling protocol is first-draw: samples are collected after water has been standing in pipes for a specified period, which maximizes the likelihood of detecting leached metals. The 90th percentile rule means that 90% of sampled sites must be at or below the action level before the system is considered in compliance. (40 CFR § 141.86)

Why copper is regulated together with lead

Copper and lead share Subpart I because they share a common exposure pathway — the corrosion of premise plumbing — and a common regulatory response: corrosion control treatment. Both contaminants leach into water that sits in distribution and building pipes. Both are addressed by adjusting the water's chemistry to reduce how aggressively it dissolves metals.

The LCRI, finalized October 8, 2024 (published October 30, 2024 at 89 FR 86416, effective December 30, 2024), changes the lead action level to 10 µg/L beginning November 1, 2027. The copper action level is not changed — it remains at 1.3 mg/L under LCRI. Utilities complying with LCRI requirements will be simultaneously complying with copper treatment technique requirements, because the corrosion control work required for lead compliance also reduces copper leaching. (EPA LCRI page)

This co-regulation also explains why the lead contaminant page and this page are structurally parallel. Both use action levels, both use the 90th percentile sampling rule, and both depend on corrosion control as the primary treatment intervention.

Treatment: corrosion control

Corrosion control treatment (CCT) is the primary mechanism utilities use to keep copper concentrations in tap water below the action level. The goal is to adjust the water's chemistry so that it deposits a thin protective scale on the interior of pipes rather than dissolving metal into the water.

Common corrosion control approaches include:

The LCRI requires systems with lead service lines to optimize CCT and potentially install enhanced CCT if 90th percentile lead results remain elevated. The copper monitoring data from the same tap samples provides a concurrent check on whether CCT is working for copper as well. (40 CFR § 141.82)

Utilities that exceed the copper action level must take escalating steps defined at 40 CFR § 141.81–141.83, beginning with enhanced corrosion control study and implementation. These steps are a treatment technique obligation, not a violation reporting obligation in the same sense as an MCL exceedance.

What utilities must disclose on the CCR

Every CCR must include copper monitoring results in the regulated contaminants table, regardless of whether the action level was exceeded. Required table fields include the contaminant name, units (mg/L), the action level (1.3 mg/L), the MCLG (1.3 mg/L), the detected level or range, and whether any action level exceedance occurred. (40 CFR § 141.153)

The source disclosure in the table must state: "Corrosion of household plumbing systems; Erosion of natural deposits." This is the federally prescribed language from Appendix A to Subpart O and cannot be paraphrased. (40 CFR Appendix A to Subpart O of Part 141)

If the system's 90th percentile tap result exceeds 1.3 mg/L, the CCR must also include the verbatim health-effects boilerplate quoted above. The boilerplate is not optional language; it is the codified text required by Appendix A to Subpart O.

Systems that have taken required actions — corrosion control, public education, or other measures — in response to an exceedance must describe those actions in the CCR. (40 CFR § 141.153(d))

For a broader overview of what the CCR must contain and how the regulated contaminants table is structured, see CCR Resources.

Last reviewed: 2026-05-03. Next scheduled review: every 6 months or after LCRI implementation milestones.