Find
Water Hardness by ZIP Code
Water hardness by ZIP code: enter a ZIP to get your county's measured hardness from USGS/EPA data, plus the utility that serves it, from EPA's service-area boundaries (44,656 systems). ZIPs outside any mapped service area get the honest answer: likely a private well, with testing guidance.
5-digit ZIP · U.S. only · your address stays in your browser
Systems
America's largest water systems
The community water systems in this dataset serve populations from a few dozen people to millions. The fifteen largest each supply more than 1.3 million residents and together reach about 35 million Americans. New York City's system is the single biggest at roughly 8.3 million people served, drawing from upstate reservoirs; Los Angeles (~4.0 million) and Chicago (~2.7 million) come next.
Population-served counts come from EPA's SDWIS inventory — a design figure for how many people a system serves, labeled approximate (~FY2021), not a live census. Surface water dominates the top of the table: fourteen of the fifteen largest draw from rivers, reservoirs, or lakes, the exception being Miami-Dade, which pumps the Biscayne Aquifer. Hardness varies system to system; where a utility publishes it, its Consumer Confidence Report is the source, and our per-system pages will carry those values as they land.
| System | State | Population served | Source |
|---|---|---|---|
| New York City System | NY | 8,271,000 | Surface |
| Los Angeles — Dept. of Water & Power | CA | 4,041,284 | Surface |
| Chicago | IL | 2,700,000 | Surface |
| Miami-Dade (MDWASA Main System) | FL | 2,300,000 | Ground |
| City of Houston | TX | 2,221,706 | Surface |
| San Antonio Water System | TX | 1,999,472 | Surface |
| Washington Suburban Sanitary Commission | MD | 1,800,000 | Surface |
| City of Baltimore | MD | 1,600,000 | Surface |
| Philadelphia Water Department | PA | 1,600,000 | Surface |
| Phoenix, City of | AZ | 1,579,000 | Surface |
| Las Vegas Valley Water District | NV | 1,502,604 | Surface |
| East Bay MUD | CA | 1,405,000 | Surface |
| San Diego, City of | CA | 1,394,515 | Surface |
| Denver Water Board | CO | 1,362,071 | Surface |
| Cleveland Public Water System | OH | 1,308,955 | Surface |
Coverage
How water service areas work
A water utility's territory is a mapped polygon, not a list of ZIP codes. EPA's Public Water System Service Area Boundaries dataset (SAB v3) draws those polygons for 44,656 community systems — more than half from authoritative state or utility sources, the rest modeled — covering about 99% of the population served by community water. This lookup resolves your ZIP to its geographic center, then finds which polygon that point falls inside.
Service areas follow pipes and pressure zones, not postal geography, so the two rarely line up. About 684 ZIP codes straddle two or more systems; for those we show every system whose boundary covers the ZIP's center, as separate cards, and you pick yours by city or system name. A ZIP can also sit mostly in one system while its center lands in a neighbor's polygon — a ZIP-centroid method trades address-level precision for full national coverage.
The result is a conservative lower bound: 50.8% of ZIP centers fall inside a mapped community system, and 70.2% of the US population lives in one of those ZIPs (EPA reports about 87% of people are served by community systems overall, so an address-level answer is more precise than this ZIP aggregate). When your ZIP's center lands outside every polygon, that is usually real — private-well country — not a gap in the data.
Utility water vs. well water
Roughly half the country's ZIP codes resolve to a community water system; the other half — 49.2% of ZIP centers — fall outside every mapped service area, which usually means private wells. The two are measured differently: a utility treats and blends its water and reports it in an annual Consumer Confidence Report, while a private well reaches your tap untreated, and no agency publishes its hardness.
If your lookup returns no utility, that is the honest signal you are likely on a well — start with your county's measured groundwater hardness above, then see well water hardness for what to test, and iron in well water if you have staining. If you are on a utility, its reported hardness (when published) and your county's measured value together bracket what comes out of your tap.
Questions
Frequently asked questions
- How hard is the water in my area?
- Enter your ZIP above and the tool shows your county's measured hardness in mg/L and grains per gallon, drawn from USGS/EPA monitoring data — the most local measured value published for your area.
- What is the water hardness in my area?
- It's the county median from USGS/EPA lab measurements, shown above once you enter a ZIP. It is an area aggregate, not a ZIP-specific reading; an address-level number would be more precise.
- Do I have hard water?
- Enter your ZIP: if your area's measured median is 120 mg/L or above, your water is classified hard or very hard on the USGS scale, which the result names for you. Below 60 mg/L it is soft.
- Is my water hard or soft?
- The result gives the plain-language band for your area — soft, moderately hard, hard, or very hard — from the county's measured median, so you get the verdict, not just a number.
- How do I find out who services water at my address?
- Enter your 5-digit ZIP above — this tool maps it to the community water system whose service area covers it, using EPA's Public Water System Service Area Boundaries (SAB v3, 44,656 systems).
- Why does my ZIP show more than one utility?
- Utility service-area boundaries don't follow ZIP-code lines, so about 684 ZIPs overlap two or more systems. Pick yours by city or system name — each is shown as its own card.
- Who is the largest water provider in the US?
- By population served, per EPA SDWA records (~FY2021), the New York City system is the largest single community water system in this dataset, at about 8.3 million people served from upstate reservoirs. Los Angeles (~4.0 million) and Chicago (~2.7 million) follow; see the full top-15 table above.
- My ZIP shows no utility — is that an error?
- No. We resolve a ZIP by its geographic center, and 49.2% of ZIP centers fall outside any mapped community water system — typically private-well country. That is the honest answer, not a failure.
- How accurate is ZIP-level lookup?
- It's a ZIP-centroid method — a conservative lower bound: 70.2% of the US population lives in a ZIP whose center falls in a mapped service area (EPA reports ~87% of people are served by community systems). An address-level answer is more precise than this aggregate.
- Where do I find my utility's exact hardness number?
- Utilities rarely print hardness in their Consumer Confidence Report; meanwhile the area's measured county hardness is shown above, and utility-reported values arrive with our water-system pages.
More: what the numbers mean · who is my water company · reading a water-quality report · test your water · the national map.
By Marko Visic, MPharm, BSc Physics. Source: EPA Public Water System Service Area Boundaries (SAB v3) + USGS/EPA county hardness. Data last verified . Methodology.
Cite this page: “Water Hardness by ZIP Code — Utility & Area Lookup.” Hard Water Map. Retrieved 2026-07-22, https://hardwatermap.com/lookup/