The lead and copper action level is the number most small-system operators misread as a limit they either passed or failed. It is not that. It is a trigger. Cross it and you are not just "over a number" — you owe your state a corrosion-control plan, a round of water quality parameter monitoring, and, where lead service lines are involved, a replacement schedule. The federal lead action level is 15 parts per billion (ppb), or 0.015 milligrams per liter, measured at the 90th percentile of tap samples collected under 40 CFR 141.80. Under the Lead and Copper Rule Improvements (LCRI), that number drops to 10 ppb. If you operate a community or non-transient non-community water system and you are not sure what your last round of tap samples showed, check your water system's compliance status free at orevant.com before you read on.
What an action level actually is
An action level is not a maximum contaminant level (MCL). An MCL is a hard legal ceiling on what is in the water at the treatment plant or in the distribution system. An action level is a health-protective line measured at the customer's tap — specifically at the 90th percentile of the samples you collect — and crossing it triggers treatment technique requirements, not just a violation flag. See the difference between an MCL and an action level.
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Here is what the 90th percentile means in practice. You sample a set of higher-risk homes: those with lead service lines, lead solder, or lead plumbing. If more than 10 percent of those homes read above the action level, your system has exceeded it. The point of the rule is not to measure your best taps; it is to measure the taps most likely to have a lead problem, and to force action when the worst 10 percent cross the line.
The two numbers you are held to
- Lead — 15 ppb (0.015 mg/L) at the 90th percentile today. The LCRI lowers this to 10 ppb (0.010 mg/L).
- Copper — 1.3 mg/L (1,300 ppb) at the 90th percentile.
The 2021 Lead and Copper Rule Revisions (LCRR) also introduced a trigger level of 10 ppb for lead — a proactive threshold below the action level that requires a system to complete corrosion control treatment, review its treatment plan, and finish its service line inventory. The LCRI, finalized in October 2024, folds that lower number into the action level itself, so the 10 ppb standard is the direction every system is heading.
What an exceedance triggers
Crossing the action level starts a fixed sequence under 40 CFR 141.80 and 141.81:
- Public notification — an action level exceedance for lead or copper is a Tier 1 notice due within 24 hours, delivered to every customer and filed with your state.
- Corrosion control treatment (CCT) — you must install or optimize treatment to reduce lead and copper leaching, or demonstrate you already have optimal treatment in place.
- Water quality parameter (WQP) monitoring — ongoing sampling of pH, alkalinity, and other parameters to prove the treatment is working.
- Source water monitoring — to determine whether the lead or copper is coming from your distribution system or your source.
- Lead service line replacement — systems with lead or galvanized-requiring-replacement lines must replace them on the LCRI schedule. See what your lead service line inventory must file, and when.
Why the unknown line is the expensive line
Under 40 CFR 141.84, a service line you have not verified is treated as lead until proven otherwise. That means a system with a pile of "unknown" lines is carrying an exceedance risk it cannot see, and a replacement obligation it has not priced. The cheapest day to resolve an unknown line is the day before it shows up as a corrosion-control finding on a sanitary survey. See what an SDWA violation actually costs in penalties.
What a small system should do this month
Do not wait for a tap sample to come back above 15 ppb. Pull your last Lead and Copper Rule round, confirm your 90th percentile, and resolve every unknown service line. A checklist points you at what to inspect; it does not replace a system-specific read of your EPA record, your sampling schedule, and your next deadlines.
FAQ
Is the lead action level the same in every state?
The 15 ppb action level (moving to 10 ppb under the LCRI) is the federal floor. States with primacy may set stricter requirements, and several already require more aggressive lead service line replacement or lower action-level thresholds. Your state primacy agency's rulebook governs on top of the federal baseline.
My system has no lead service lines. Do I still sample for lead and copper?
Yes. The Lead and Copper Rule applies to community and non-transient non-community systems regardless of whether they have known lead lines, because lead can also come from lead solder and brass fixtures inside buildings. Your sampling site selection and frequency are set by your state primacy agency.
What is the difference between the action level and the trigger level?
The action level (15 ppb today, 10 ppb under the LCRI) is the enforcement line that triggers corrosion control treatment, public notification, and monitoring. The trigger level (10 ppb under the LCRR) is a lower, proactive threshold that requires a system to complete corrosion control treatment and finish its inventory before an exceedance happens.