Data sources: EPA SDWIS, EPA LCR, EPA Radon Zones, FEMA OpenFEMA Last updated: March 2026

What Is the Home Safety Score?

The Home Safety Score is a composite rating from 0 to 100 that summarizes measurable environmental risk factors for any U.S. ZIP code. It combines four dimensions of home safety: water quality, lead contamination, radon exposure, and flood risk.

Higher scores indicate safer conditions. A score of 85 means low risk across most dimensions. A score of 45 means multiple risk factors warrant attention.

Every score is derived entirely from federal government data — EPA, FEMA, and CDC sources. We do not accept payment to influence scores, and no real estate or utility company has any input into the calculation.

The score is designed to be a screening tool, not a definitive assessment. It tells you which risks to investigate further for a specific ZIP code. For a detailed look at your area, check your ZIP code report.

For the full technical methodology, see the methodology page.

The Four Components

The Home Safety Score has four equally weighted components:

Component	Max Points	Data Source	What It Measures
Water Quality	25	EPA SDWIS	Drinking water regulation violations
Lead Level	25	EPA Lead and Copper Rule	90th percentile lead at the tap
Radon Risk	25	EPA Radon Zones	County-level radon potential
Flood Risk	25	FEMA OpenFEMA NFIP Claims	Historical flood insurance claims

When FEMA flood data is not available for a ZIP code (because no claims have been filed or few properties carry flood insurance), the score recalculates using three components at 33 points each, maintaining the 0–100 scale.

Water Quality Sub-Score

What It Measures

The water quality component evaluates Safe Drinking Water Act (SDWA) violations reported by public water systems serving the ZIP code.

Data Source

EPA Safe Drinking Water Information System (SDWIS) — the federal database where all public water systems report compliance data. Updated quarterly.

How It's Calculated

The sub-score starts at the maximum (25 points) and deducts points based on:

• Health-based violations (MCL exceedances, treatment technique failures) — largest deductions
• Monitoring and reporting violations (missed tests, late reports) — smaller deductions
• Resolved vs. unresolved — active violations receive full weight (1.0x); resolved violations receive reduced weight (0.25x) because communities that fix problems should not be penalized the same as those with ongoing failures
• Recency — more recent violations carry more weight than older ones

ZIP-to-Water System Mapping

A single ZIP code may be served by multiple public water systems — and a single water system may serve multiple ZIP codes. When a ZIP has multiple systems, we aggregate violations across all systems. This means a ZIP code with one large compliant system and one small system with violations will still show the violations in the score.

What It Doesn't Measure

• Unregulated contaminants — PFAS monitoring is still being phased in; microplastics, pharmaceuticals, and many emerging contaminants are not in SDWIS
• Private well water — 43 million Americans on wells are not in SDWIS. If your ZIP is served primarily by wells, the water quality component may not reflect your water situation
• Water quality AT your tap — SDWIS measures compliance at the system level. Your household plumbing (lead, copper) is not captured here

Lead Level Sub-Score

What It Measures

The lead component evaluates the 90th percentile lead level from Lead and Copper Rule (LCR) tap water sampling conducted by the water system.

Data Source

EPA Lead and Copper Rule sampling results — water systems collect samples from a subset of high-risk homes (those with lead service lines, lead solder, or lead fixtures). The 90th percentile value is the key metric: if this value exceeds 15 ppb, the system is in violation.

How It's Calculated

The sub-score maps the 90th percentile lead level to a score:

• Not detected / <1 ppb — full 25 points (excellent)
• 1–5 ppb — 20–25 points (low but detectable)
• 5–15 ppb — 10–20 points (moderate risk)
• >15 ppb — 0–10 points (exceeds action level)

When a ZIP code is served by multiple systems, we use the primary system (largest population served) for the lead level, since 90th percentile values are system-specific.

What It Doesn't Measure

• Your specific home's lead level — the 90th percentile is a system statistic. Your home may be higher (if you have lead plumbing) or lower (if you have plastic pipes)
• Lead service line presence — the score doesn't tell you whether YOUR connection is lead. Check your utility's service line inventory
• Internal plumbing lead — solder, fixtures, and in-building pipes are not captured by system-level sampling

To assess your personal lead risk: Lead Risk Calculator and lead guide

Radon Risk Sub-Score

What It Measures

The radon component reflects the EPA's county-level radon zone classification — a geological assessment of predicted indoor radon levels.

Data Source

EPA Map of Radon Zones — classifies every U.S. county into Zone 1 (high: ≥4 pCi/L predicted), Zone 2 (moderate: 2–4 pCi/L), or Zone 3 (low: <2 pCi/L). Based on geological surveys, indoor radon measurements, and building type data.

How It's Calculated

Radon Zone	Sub-Score	Interpretation
Zone 3 (low)	25 points	Low predicted radon
Zone 2 (moderate)	15 points	Moderate — testing recommended
Zone 1 (high)	5 points	High predicted radon — testing strongly recommended

What It Doesn't Measure

• Your specific home's radon level — zone classification predicts the average for the county, but individual homes vary dramatically based on foundation type, soil, and ventilation
• Radon in water — the zone classification is based on indoor air measurements, not groundwater radon. Well water users in Zone 1 areas should also test their water
• Post-mitigation levels — if your home has a radon mitigation system, your actual exposure is likely far below the zone average

Testing is the only way to know your home's radon level. Radon guide

Flood Risk Sub-Score

What It Measures

The flood component evaluates historical flood insurance claims in the ZIP code from FEMA's National Flood Insurance Program.

Data Source

FEMA OpenFEMA NFIP Redacted Claims v2 — records of every flood insurance claim filed under the NFIP, including claim amount, date, and ZIP code. Updated as claims are processed.

How It's Calculated

The sub-score evaluates:

• Number of claims in the ZIP code (normalized by estimated housing units)
• Total claim payments — severity indicator
• Recency — recent claims weighted more heavily
• Repetitive loss patterns — areas with repeated flooding receive larger deductions

A ZIP code with zero claims receives full points. A ZIP code with many recent claims, high total payouts, and repetitive loss patterns receives the lowest scores.

What It Doesn't Measure

• Properties WITHOUT flood insurance — NFIP claims only capture insured properties. Flooding that occurred in properties without coverage is not captured. This is a significant limitation in areas where flood insurance uptake is low
• FEMA flood zone designation — the score uses actual claim data, not theoretical flood zone maps. This can differ from the FEMA zone — some Zone X areas have significant claims, and some Zone A areas may have few claims
• Future flood risk — the score reflects historical patterns. Climate change may increase flood risk in areas with low historical claims

For detailed flood risk assessment: Flood risk guide

Grading Scale

Score Range	Grade	Interpretation
90–100	A+	Excellent — low risk across all dimensions
80–89	A	Very good — minor risks in one area
70–79	B	Good — one or two moderate risk factors
60–69	C	Fair — notable risks that warrant attention
50–59	D	Below average — multiple risk factors
Below 50	F	Significant risks across multiple dimensions

Important context: A grade of C or D does not mean the area is unsafe to live in. It means specific risk factors exist that you should investigate and, where possible, mitigate. A home with a score of 55 and a quality radon mitigation system, a water filter, and flood insurance can be as safe as a home with a score of 90.

Limitations

The Home Safety Score is useful but imperfect. Important limitations:

1. ZIP-level granularity — a ZIP code can span different water systems, geological zones, and flood areas. The score is an aggregate, not property-specific

2. Data lag — EPA data updates quarterly to annually. A violation that occurred last month may not yet appear in the score

3. Not all risks are captured — the score does not include: air quality, proximity to Superfund sites, soil contamination, wildfire risk, earthquake risk, or social/economic factors

4. Well water gap — 43 million Americans on private wells are not represented in the water quality or lead components

5. Flood data bias — NFIP claims data only captures insured properties. Areas with low insurance uptake may appear safer than they are

6. Radon is county-level — the radon zone classification applies to the entire county, not individual neighborhoods or properties

7. No weighting for vulnerability — the score does not adjust for the presence of children, elderly residents, or immunocompromised individuals who may be more susceptible to the risks measured

How to Use Your Score

For Homebuyers

1. Look up the ZIP as an initial screen when evaluating properties
2. Compare ZIP codes you're considering — the score makes relative comparison easy
3. Dig into the component breakdown — a score of 65 could mean one bad component or several mediocre ones
4. Use the component scores to prioritize testing and mitigation during your home inspection

For Current Homeowners

1. Identify which components are dragging your score down
2. Take action on the lowest-scoring component:
   • Low water quality score → check your CCR, consider a filter
   • Low lead score → test your tap, install a certified filter
   • Low radon score → test your home, mitigate if above 4 pCi/L
   • Low flood score → check your flood zone, get insurance, implement mitigation
3. Re-check annually — data updates as new violation and claim records are published

For Real Estate Professionals

The score provides a data-driven, neutral way to discuss environmental factors with buyers. It is based entirely on federal data and is not a substitute for professional environmental assessments, but it highlights which assessments are most relevant for a given area.

FAQ