Grading Methodology

How we calculate water quality grades from EPA data

Grade Scale

A: 90-100 points

Excellent water quality with minimal contaminants and violations

B: 80-89 points

Good water quality with few concerns

C: 70-79 points

Moderate water quality - filtration may be beneficial

D: 60-69 points

Poor water quality - filtration is recommended

F: 0-59 points

Severe water quality issues - filtration is essential

Scoring Components

Our grade is calculated from five key metrics:

1. Contaminant Count (25 points)

The number of unique contaminants detected in the water system. More contaminants = lower score. We track over 300 drinking water contaminants regulated under the Safe Drinking Water Act.

2. Violation History (25 points)

The frequency and recency of Safe Drinking Water Act violations. Systems with repeat violations score lower. We analyze violations from the past 5 years.

3. Contaminant Severity (25 points)

The health impact of detected contaminants. Some contaminants (like lead) have more severe health effects than others. We weight violations accordingly.

4. System Compliance (15 points)

How well the system complies with EPA monitoring and testing requirements. Systems that skip required testing score lower.

5. Enforcement History (10 points)

Whether the EPA or state has taken enforcement action against the system. Enforcement actions indicate serious compliance issues.

Data Processing

  1. Download EPA ECHO bulk data and Envirofacts API data quarterly
  2. Identify all active community water systems in each zip code
  3. Extract violations from the Safe Drinking Water Act violations table
  4. Categorize contaminants by type and severity
  5. Calculate per-zip-code aggregate statistics
  6. Apply grading algorithm to generate A-F grades
  7. Store results in our database with timestamps for historical tracking

Limitations & Disclaimers

  • Our grades are based on public EPA data, not independent testing
  • Grades represent system-wide averages, not neighborhood-specific quality
  • Some zip codes may have multiple water systems with different grades
  • We update quarterly, but EPA data may be delayed 6+ months
  • Contaminant levels below the MCL are still reported
  • This is educational information, not a professional water audit

Questions About Our Methodology?

We welcome feedback and questions about our grading system. Our goal is transparency and accuracy. Contact us with any concerns.