EPA AirData + SDWIS/ECHO
Compare Two ZIP Codes
Enter two ZIP codes and see their air and water scores side by side, with one plain sentence on which comes out ahead. Same EPA data as the single-ZIP score, same weighting applied to both.
Showing Los Angeles County, CA vs New York County, NY
| EPA AirData + SDWIS/ECHO | ZIP 90210Los Angeles County, CA | ZIP 10001New York County, NY |
|---|---|---|
| Composite | 63 Mixed | 83 Mixed |
| Air score | 27 | 66 |
| 90th percentile AQI | 147 · Unhealthy for sensitive groups | 69 · Moderate |
| Water score | 99 | 100 |
| Water systems / people served | 199 · 10,058,958 | 1 · 8,271,000 |
| Unresolved health-based violations | 21 | 0 |
Both ZIP codes are scored under the same weights, so the comparison stays fair: air 50% / water 50%, and an unresolved health-based violation costs 25 points.
Informational only, not professional advice. This tool summarises public EPA compliance and monitoring records. It is not a health assessment, a water test, or a substitute for testing the water at a specific address.
How this is calculated
Both ZIP codes are scored with the exact same formulas and the exact same weights as the Air & Water Score by ZIP Code tool — this page just runs the lookup twice and puts the results next to each other, plus the one comparison sentence. The full derivation, every source, and the stated coverage limits live on that page; this section summarises.
Air
air = 100 − (90th percentile AQI ÷ 2), floored at 0
From EPA AirData's annual AQI by county file for 2025. A county with no monitor shows no air score for either side — never an estimate from a neighbouring county.
Water
penalty per system = 25×(open health-based)
+ 8×(resolved health-based)
+ 4×(open monitoring/reporting)
+ 1×(resolved monitoring/reporting)
capped at 100
water = 100 − (average penalty, weighted by people served)From EPA SDWIS/ECHO (2026Q2), violations counted over the last 5 years. These four coefficients are our judgement, which is why they're adjustable — and both ZIP codes always share whatever values are set, so the comparison stays apples-to-apples.
Composite
score = 50% × air + 50% × water
Shown only when both halves exist for that ZIP. Where one side is missing a half, the table shows “—” for it and the plain sentence falls back to comparing whichever halves both ZIP codes actually have.
Sources
Last reviewed: September 2026 · Data in use: SDWIS 2026Q2, AirData 2025 · Dataset built 2026-09-02
Frequently asked questions
How are the two scores calculated?
The same way as the single-ZIP tool: an air subscore from EPA AirData's annual 90th-percentile AQI for the county, and a water subscore from EPA SDWIS/ECHO violation records for the community water systems serving that county, weighted by population served. See the Air & Water Score by ZIP Code page for the full formulas and sources.
Why does one ZIP code show no air score?
Because there is no EPA air quality monitor in that ZIP's county. Monitors cover roughly half of US counties by ZIP count, though most people live in a monitored one. Where there's no monitor, we show no air score rather than estimating one from a neighbouring county.
Do both ZIP codes use the same assumptions when compared?
Yes, always. The weighting controls (how much a violation costs, how air and water are combined) apply to both sides at once — comparing two places under different weights would be comparing different things, not the places themselves.
How current is this data?
The same vintage as the single-ZIP tool: drinking water violations from the EPA SDWIS/ECHO bulk download (refreshed quarterly) and air quality from EPA AirData's annual AQI summary (the latest complete year). The exact quarter and year in use are printed below.
Related tools
Enter a ZIP code and get one score for the air and one for the drinking water, each traced to an EPA record.
Open tool →Drinking Water by UtilityLook up your water utility by name and see every violation on its EPA record for the last five years.
Open tool →Cleanest Air by StateEvery state ranked by how clean its measured air is, with the monitored counties behind each rank.
Open tool →Worst Water Violations by StateEvery state ranked by the drinking-water violations on its utilities' EPA records, worst first, down to the county.
Open tool →Best & Worst Counties for Air and Water QualityThe 100 best and 100 worst US counties for air and water together, with a ZIP code to try for each.
Open tool →Cleanest Drinking Water by StateEvery state ranked by the drinking-water violations on its utilities' EPA records, cleanest first.
Open tool →Air Quality Trend by CountyTen years of EPA air readings for any county, and a plain call on whether it has gotten better, worse, or stayed the same.
Open tool →