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AquaCensus

Methodology & data sources

Dataset updated .

Source data

AquaCensus is built from the U.S. EPA's Safe Drinking Water Information System (SDWIS), obtained through the EPA ECHO bulk data service (SDWA dataset). The inventory covers 142,891 active public water systems — system name, PWSID, system type, primacy agency, population served, service connections, owner type, primary water source and served geography (city, county, state, ZIP).

SDWA violation and enforcement records (also from EPA ECHO) are shown on each system profile (most recent first) and are available in full through the API, the MCP server and the national violations data file.

Refresh cadence

EPA publishes the SDWA bulk dataset quarterly. AquaCensus re-syncs on that cadence with id-stable upserts keyed on PWSID, and every page carries a machine-readable "Dataset updated" timestamp plus Dataset JSON-LD with dateModified.

Definitions & caveats

  • Only systems with EPA activity status "A" (active) are indexed; inactive systems resolve but are excluded from search indexing and sitemaps.
  • "Population served" is the figure each system reports to its primacy agency; summing across systems double-counts people served by wholesalers and purchasers.
  • Geography comes from EPA's geographic-areas records. Where a system reports several counties, its profile lists every county EPA records for it, in the order they were reported; state and county counts and county lists file each system under the first county reported, and county pages also list multi-county systems that serve them. The city shown is the first city reported.
  • SDWIS, the EPA dataset AquaCensus is built from, does not include service-area boundaries or coordinates for water systems. EPA separately publishes a Public Water System Service Areas dataset that combines EPA-modeled boundaries with boundaries supplied by water systems and states (version 3, March 2026). AquaCensus does not use those boundaries yet, so it cannot match a street address to a system.
  • AquaCensus covers drinking water systems regulated under the Safe Drinking Water Act. It does not cover sewer or wastewater utilities, which are regulated under a different law and are not in this data. Some utilities provide both services and include "sewer" in their name; their AquaCensus profile describes the drinking water system only.
  • Violation and contaminant codes are EPA's SDWIS codes. Pages show EPA's descriptions from its SDWA reference tables with the code alongside. Monitoring and reporting violations mean a required test or report was missed or late, not that a contaminant was found; health-based violations are those of a legal limit or a required treatment technique.
  • AquaCensus is screening data, not compliance or health advice. For current compliance status, consult EPA ECHO or the system's Consumer Confidence Report.

Licensing & attribution

Underlying EPA records are U.S. public data. AquaCensus pages and derived aggregates may be cited with attribution to "AquaCensus (aquacensus.com)". For bulk or API access, contact kenny@hyder.me.