TapScore

Methodology

Data Source

All data comes from the EPA's Safe Drinking Water Information System (SDWIS), which tracks compliance data for all public water systems in the United States. We focus on active Community Water Systems (CWS) — systems that serve at least 15 connections used by year-round residents.

Safety Grade Calculation

Safety grades are calculated based on a water system's violation record over the most recent 5-year period. We consider two key factors:

  • Recent violations: Total number of violations in the past 5 years
  • Health-based violations: Violations of health-based standards (Maximum Contaminant Levels, treatment techniques)
A

Grade A — Safe

Zero violations in the past 5 years. The system has maintained full compliance with all EPA standards.

B

Grade B — Good

1-2 recent violations, none health-based. Minor monitoring or reporting issues only.

C

Grade C — Fair

Up to 5 recent violations, or 1 health-based violation. Some compliance concerns.

D

Grade D — Poor

2-5 health-based violations. Significant compliance issues that may affect water safety.

F

Grade F — Unsafe

6 or more health-based violations. Serious and persistent water quality issues.

Violation Types

The EPA tracks several types of violations:

  • Health-based violations: Exceeding Maximum Contaminant Levels (MCLs), treatment technique failures, or failure to meet required treatment standards. These directly affect water safety.
  • Monitoring violations: Failure to conduct required water quality testing on schedule.
  • Reporting violations: Failure to report test results or other required information to the state or EPA.
  • Public notification violations: Failure to notify the public about water quality issues as required.

Limitations

  • Our grades are based on violation records only, not actual contaminant concentration levels.
  • Some violations may have been resolved. A violation record means the system was non-compliant at some point, not necessarily that it currently is.
  • Data is updated periodically from the EPA and may not reflect the most recent compliance actions.
  • Private wells and non-community water systems are not included.

Data Update Frequency

We fetch updated data from the EPA SDWIS database periodically. The EPA updates SDWIS quarterly with data submitted by state primacy agencies. There may be a lag between when a violation occurs and when it appears in the federal database.