IRS Income Data vs Water Quality by ZIP Code

Data source: ZipCheckup analysis of IRS SOI, Census ACS 2023, EPA SDWIS

Every year, the IRS publishes something most taxpayers never see: a complete breakdown of income data by ZIP code. How many returns were filed. The total adjusted gross income. The distribution across income brackets. It covers 27,589 ZIP codes — and when you cross-reference it with water quality data, the pattern that emerges is not what you'd expect.

The Counterintuitive Finding

Conventional wisdom says wealthier areas have better everything — better schools, better infrastructure, better water. The data tells a different story.

We divided all 30,619 ZIP codes with both income and water safety data into five groups by median household income and calculated the average water safety score for each:

Read that again: the wealthiest ZIP codes have the lowest average safety scores. The gap between the bottom and top quintile is 7.4 points — not enormous, but the direction is the opposite of what most people assume.

331 Wealthy ZIPs With F Grades

The most striking cases sit at the extremes. Among ZIP codes where median household income exceeds $150,000, we found 331 with F safety grades — the lowest possible rating.

These aren't borderline cases. They include some of the wealthiest addresses in the country:

Meanwhile, some of the lowest-income ZIP codes have surprisingly clean water:

ZIP 16501 in Erie, Pennsylvania — with a median income of just $14,579 — scores 79 on water safety. That's a solid B grade. Greenwich Village, with income ten times higher, scores 13. An F.

Why Income Doesn't Predict Water Quality

Three structural factors explain this pattern:

1. Infrastructure Age vs. Neighborhood Age

Many of America's wealthiest neighborhoods sit atop some of its oldest water infrastructure. Manhattan's water mains date to the early 1900s. Affluent Boston suburbs rely on systems built in the 1940s and 1950s. When these communities became wealthy, they inherited pipes that were already decades old.

Newer, lower-income suburbs — built in the 1990s and 2000s with modern plumbing codes — often have better physical infrastructure despite lower property values.

2. Geological Reality

Natural contaminants — arsenic, radon, uranium — follow rock formations, not real estate markets. Wealthy exurban communities in New England, the Mid-Atlantic, and parts of California sit on geological formations that leach contaminants into groundwater regardless of what the houses above cost.

3. The Private Well Gap

The IRS data shows that ZIP codes with incomes above $150K have a much higher rate of private well usage than the national average. Private wells aren't covered by the Safe Drinking Water Act. No mandatory testing. No EPA enforcement. No violation tracking. A $3 million home on a private well may have water that has literally never been tested for PFAS or lead.

Even among regulated public systems, transparency is uneven: across the 5,572 utilities tracked in the CCR Rich Dataset, only 51.2% disclose a customer-service phone number and 27.9% a website in their CCR — meaning wealth and water-quality visibility don't track each other any more closely than wealth and water quality itself.

The Environmental Justice Angle

While wealthier areas have worse average scores, the consequences fall harder on lower-income communities. When we look at all F-grade ZIP codes across the income spectrum:

• 2,806 F-grade ZIPs are below the national median income ($65,000)
• 4,388 F-grade ZIPs are above it

Both groups face water quality problems, but lower-income households spend a larger percentage of their income on water, are less likely to afford filtration systems ($200–$5,000 depending on type), and have less political leverage to demand infrastructure upgrades. This compounding vulnerability is documented across Hispanic-majority ZIPs in our Hispanic ZIP risk index.

The IRS data reveals that water quality problems are genuinely universal — they cross every income bracket. But the ability to respond to those problems is not.

What the IRS Data Shows About Your ZIP

Every ZIP code on ZipCheckup now incorporates IRS income data alongside water quality metrics. Your report shows:

• Median household income and how it compares nationally
• Income bracket distribution from IRS SOI data (27,589 ZIPs)
• Water safety score — independent of income, based on EPA violation data
• Environmental burden — industrial facilities, contamination sources, and infrastructure age

The correlation between income and water safety is weaker than the correlation between infrastructure age and water safety. If you want to predict a ZIP code's water quality, ask when the pipes were installed — not what the houses cost.

Check your ZIP code now →

Methodology: Income data from IRS Statistics of Income (SOI) ZIP-level data (27,589 ZIPs) and Census American Community Survey 2023 5-year estimates (30,619 ZIPs). Water safety scores from ZipCheckup's composite analysis of EPA SDWIS violations, ECHO enforcement records, contaminant levels, lead risk factors, and flood exposure for 29,218 ZIP codes. Quintile boundaries set at $40K, $60K, $85K, and $120K median household income.