Detection vs Violation: What Water Test Terms Mean

These terms are easy to mix up.

Detection vs violation

• Detection: a lab found a substance. Many substances are detected at levels below the legal limit.
• MCL (legal limit): the highest level EPA allows. Going over it, usually as an average over time, is a violation.
• MCLG: a health goal with no enforcement. It can be zero (for lead it is zero).
• Action level (lead and copper): a trigger for extra steps such as corrosion control and public education. Exceeding it is not a violation by itself.
• Monitoring or reporting violation: a test or report was late or missing. It does not by itself mean a contaminant was too high.

Sources

• EPA: National Primary Drinking Water Regulations