The index intentionally separates measurable geography from property-specific claims.
30% Air snapshot + 30% drinking-water compliance + 20% climate moisture pressure + 20% housing-age maintenance proxy.
AirNow current reporting-area AQI is converted to a 0–100 component score. Current AQI is volatile and is the main reason rankings can move between updates.
EPA ECHO/SDWIS is queried for active community water systems by state and for systems with current health-based violations. It does not test water at an individual tap.
NOAA 1991–2020 monthly station normals provide warm-season temperature and precipitation. These produce a climate moisture-pressure proxy, not a mold probability model.
Census ACS B25035_001E provides median year structure built for a city/place. Housing age is only a maintenance-age proxy and is not evidence that older buildings contain a particular hazard.
When a source temporarily fails, the updater preserves the prior observed value and marks source coverage. Missing live observations are never replaced with newly invented values.
The score is an editorial composite. Different weights would produce different rankings, so component values are published alongside the overall score.