EPA SDWIS — how to read drinking-water violations and what they actually mean

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.