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EPA SDWIS — how to read drinking-water violations and what they actually mean
The EPA Safe Drinking Water Information System (SDWIS) records every violation by every public water system in the United States. Most violations sound alarming but are reporting or monitoring lapses, not contamination. Knowing the difference matters.
Published 2026-04-25 · Last reviewed 2026-05-13 · methodology
Three categories of SDWIS violations
Health-based: a measured contaminant exceeded the federal Maximum Contaminant Level (MCL). Examples: lead above 15 ppb action level, total trihalomethanes above 80 ppb. Public notification required within 24h–30 days depending on contaminant.
Monitoring: the utility didn't run the required test on time. Common when staffing or equipment fails. Doesn't mean water was contaminated — but means you don't know.
Reporting: the utility ran the test but failed to submit results to the state on time. Paperwork issue.
What an MCL is
Maximum Contaminant Level — the federal legal limit for a contaminant in tap water, set by EPA under the Safe Drinking Water Act.
MCLs are based on the lowest level achievable with available technology, weighted against cost. They're not zero-risk thresholds for every contaminant.
Some MCLs have action levels (like lead's 15 ppb) that trigger public notice + required corrective action even though they're not strict 'violations' under SDWIS terminology.
What triggers a public notice
Tier 1 (urgent): potential immediate health impact. E. coli, chemical spill, nitrate > 10 ppm. 24h notice required.
Tier 2: ongoing exceedance. Quarterly notice required for the duration of violation.
Tier 3: monitoring/reporting issues. Annual Consumer Confidence Report (CCR) only.
Most ZIPs get a Tier 3 notification once a year inside their water bill — that's the CCR, and it's a useful read.
What zipradar shows
We pull SDWIS for the community water system serving each ZIP. Pages show: most recent health-based violations (last 3 years), most recent lead/copper sampling results, and a link to the CCR.
For private wells, SDWIS doesn't apply — those are state-by-state. Most state health departments offer free testing or subsidized labs.
Related zipradar topics
Glossary terms used here
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