Action Level
A regulatory threshold that triggers required treatment or other corrective action when exceeded, used for lead (15 ppb) and copper (1.3 mg/L) instead of a traditional MCL.
How It Works
Action levels differ from MCLs because lead and copper enter water primarily from household plumbing, not from the water source or treatment plant. Water systems monitor lead and copper at customer taps (not at the treatment plant) and calculate the 90th percentile. If the 90th percentile exceeds the action level, the system must take corrective action: optimizing corrosion control treatment, conducting public education, and potentially replacing lead service lines. The 2024 Lead and Copper Rule Improvements lowered the action level for lead to 10 ppb and set a trigger level of 15 ppb, requiring more aggressive action at higher levels.
Related Terms
- Lead in Drinking Water, Lead contamination from aging pipes, solder, and fixtures, there is no safe level of lead exposure, and even low levels can cause irreversible developmental damage in children.
- Maximum Contaminant Level (MCL), The highest level of a contaminant allowed in drinking water, set by the EPA and enforceable by law. Exceeding the MCL triggers a health-based violation.
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About This Definition
This definition is part of the IsWaterSafe Drinking Water Safety Glossary, 22 terms explaining water contaminants, treatment methods, and safety standards. Written for homeowners, renters, journalists, and public health professionals.