Home Safety Score: How It Works
One screening score, three domains, and explicit coverage
Data sources: EPA SDWIS, EPA ECHO, EPA UCMR5, EPA Radon Zones, EPA AirData Last updated: August 2026
ZipCheckup guide: A homeowner-friendly guide to Home Safety Score model 4.0.0, its four accepted inputs, coverage, grades, context verticals, and limitations.
The short version
Home Safety Score model 4.0.0 summarizes four accepted evidence inputs across three equally weighted domains:
| Domain | Inputs |
|---|---|
| Drinking water | EPA SDWIS system identity, accepted ECHO SDWA violation lifecycle evidence, and UCMR5 PFAS screening |
| Indoor environment | EPA county radon zone |
| Outdoor environment | EPA annual county AQI |
The result is a 0-100 screening score. A higher score means lower measured concern within these inputs. It does not mean that every hazard is low or that a specific property is safe.
Why coverage matters
The score appears only when all four inputs are available. If a ZIP lacks qualifying PFAS monitoring, direct public-water evidence, a radon mapping, or sufficient annual AQI coverage, the tool shows the score as unavailable.
Missing data is not treated as zero risk. The remaining components are not silently given more weight.
How the domains work
Water compliance and PFAS are averaged into one drinking-water domain. Radon forms the indoor-environment domain. Annual AQI forms the outdoor-environment domain. The three domain scores are averaged equally.
This structure keeps drinking water important without turning a Home Safety Profile into a water-only product.
Grades
| Score | Grade |
|---|---|
| 85-100 | A |
| 70-84 | B |
| 55-69 | C |
| 40-54 | D |
| 0-39 | F |
A grade is a compact summary of the current model, not a pass/fail inspection.
What about the other home-safety risks?
ZipCheckup maintains a broader Home Safety Profile with 17 baseline verticals and room for future additions. Flood history, lead, wildfire, earthquake and seismic risk, mold, Superfund proximity, infrastructure, housing, school health, environmental justice, nuclear proximity, bridge safety, and CO/gas can appear as separate context.
Those cards do not change model 4.0.0 unless a later version formally admits them. New verticals begin as candidates or context, must pass source and coverage gates, and cannot reuse evidence already counted by another component. A replacement source within one vertical must form an explicit linear supersession chain.
How to use the result
- Check whether the score has complete coverage.
- Review each component instead of relying only on the grade.
- Use the broader Home Safety Profile to investigate hazards outside the score.
- Confirm property-specific conditions with appropriate testing, inspection, official maps, and professionals.
For formulas, source limitations, and version history, see the full methodology.