Home Safety Score Methodology

Version 1.0 — Last updated: March 16, 2026

What Is the Home Safety Score?

The Home Safety Score is a composite rating from 0 to 100 that summarizes three measurable risk factors for any U.S. ZIP code: water quality, lead contamination, and radon exposure. Higher scores indicate safer conditions.

Every score is derived entirely from federal government data. We do not accept payment to influence scores or rankings.

Three Components

The score is the sum of three equally weighted components, each worth 0–33 points.

1. Water Quality (0–33 points)

Source: EPA Safe Drinking Water Information System (SDWIS)

Measures compliance of public water systems serving the ZIP code.

Health-based violations (Maximum Contaminant Level exceedances, treatment technique failures) are weighted more heavily than monitoring or reporting violations because they indicate actual contamination rather than paperwork gaps.

2. Lead Level (0–33 points)

Source: EPA Lead and Copper Rule (LCR) Sample Results

Uses the 90th percentile lead level (PB90) from the most recent sampling round at the primary water system.

The EPA Action Level for lead is 0.015 mg/L (15 parts per billion). Levels above this trigger required remediation. When no sampling data exists for a ZIP code’s water system, we assign a neutral score of 22 rather than penalizing or rewarding the absence of data.

3. Radon Risk (0–33 points)

Source: EPA Map of Radon Zones

Uses the EPA’s county-level radon zone classification (3,138 counties mapped).

Radon is the second leading cause of lung cancer in the U.S. Zone 1 counties have predicted average indoor radon levels above the EPA’s recommended action level of 4 pCi/L.

Grading Scale

Calculation Example

ZIP 60172 (Roselle, IL):

• Water Quality: 1 health violation → 33 − 5 = 28 points
• Lead Level: PB90 = 0.010 mg/L → 33 × (1 − (0.010 − 0.005) / 0.010) = 17 points
• Radon: DuPage County, Zone 1 (High) → 0 points
• Total: 45 → Grade D

Limitations

• Data freshness: EPA SDWIS and LCR data may lag 30–90 days behind real-time conditions. Our system updates daily, but upstream data depends on utility reporting schedules.
• Geographic resolution: Water quality and lead data are linked to public water systems, not individual homes. Your home’s plumbing age, condition, and private well status are not reflected.
• Radon zones are county-level averages. Actual radon levels can vary significantly between neighboring homes. The EPA recommends testing every home regardless of zone.
• Three factors only. The current score does not include flood risk, air quality, soil contamination, or other environmental hazards. We plan to add components as reliable data sources become available.
• No data ≠ safe. When lead or radon data is unavailable for a ZIP code, we assign a neutral score (22/33) rather than assuming safety. This is clearly marked on each page.
• Not a health assessment. The Home Safety Score is an informational tool based on public data. It is not a substitute for professional water testing, home inspection, or medical advice.

Data Update Schedule

Score History

Starting March 2026, we log daily snapshots of every ZIP code’s score. Over time, this allows tracking whether water quality in your area is improving or declining. Score History data cannot be recreated retroactively — it accumulates from the day we begin recording.

Corrections and Feedback

If you believe a score is inaccurate, or if you have questions about the methodology, contact us at contact@zipcheckup.com. We investigate all reports and publish corrections when warranted.

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