Water System snapshot · Population served
Largest US Water Systems by Population Served
25 ranked water systems by population served, from a fixed snapshot on 2026-09-16 (data cutoff 2024-12-31). Shown in the snapshot's published order.
A ranking is not a safety verdict
This compares one published metric for one entity class. It does not summarize everything about a system, and it is not the water at a household tap.
Snapshot 2026-09-16 · cutoff 2024-12-31
Methodology and limitations
How this snapshot is built
Public water systems ranked by the population they serve, from the EPA SDWIS record. Included to orient readers to the systems whose records affect the most people.
Reading the order
Population figures are as reported to EPA and can lag real service-area changes. Size is not a quality signal.
Exclusions
3,804 excluded. Only cities with a computed Purity Score and a resolved serving system are eligible; all others are excluded.
The ranking
Each row links to the water system’s full evidence record. Rows appear in the snapshot’s published order — a comparison of one measure (population served), not an overall safety order.
| # | Water System | Population served | On record | |
|---|---|---|---|---|
| 1 | NEW YORK CITY SYSTEMNew York City, NY | 8 271 000 served | Purity Score 84 / 100 | |
| 2 | LOS ANGELES-CITY, DEPT. OF WATER & POWERLos Angeles, CA | 3 875 566 served | Purity Score 90 / 100 | |
| 3 | CITY OF HOUSTONHouston, TX | 2 970 543 served | Purity Score 91 / 100 | |
| 4 | CHICAGOChicago, IL | 2 721 308 served | Purity Score 88 / 100 | |
| 5 | SAN ANTONIO WATER SYSTEMSan Antonio, TX | 2 643 729 served | Purity Score 95 / 100 | |
| 6 | MDWASA - MAIN SYSTEMMiami, FL | 2 377 460 served | Purity Score 44 / 100 | |
| 7 | WASHINGTON SUBURBAN SANITARY COMMISSIONWashington Suburban Sanitary Commission, MD | 1 900 000 served | Purity Score 100 / 100 | |
| 8 | PHOENIX CITY OFPhoenix, AZ | 1 695 000 served | Purity Score 91 / 100 | |
| 9 | CITY OF BALTIMOREBaltimore, MD | 1 600 000 served | Purity Score 96 / 100 | |
| 10 | PHILADELPHIA WATER DEPARTMENTPhiladelphia, PA | 1 600 000 served | Purity Score 52 / 100 | |
| 11 | LAS VEGAS VALLEY WATER DISTRICTLas Vegas, NV | 1 539 277 served | Purity Score 83 / 100 | |
| 12 | EAST BAY MUDEast Bay Mud, CA | 1 442 800 served | Purity Score 100 / 100 | |
| 13 | SAN DIEGO, CITY OFSan Diego, CA | 1 385 379 served | Purity Score 100 / 100 | |
| 14 | DALLAS WATER UTILITYDallas, TX | 1 356 479 served | Purity Score 65 / 100 | |
| 15 | CLEVELAND PUBLIC WATER SYSTEMCleveland, OH | 1 308 955 served | Purity Score 97 / 100 | |
| 16 | COLUMBUS PUBLIC WATER SYSTEMColumbus, OH | 1 305 946 served | Purity Score 63 / 100 | |
| 17 | DENVER WATER BOARDDenver, CO | 1 287 000 served | Purity Score 93 / 100 | |
| 18 | CHARLOTTE WATERCharlotte, NC | 1 163 701 served | Purity Score 93 / 100 | |
| 19 | SEATTLE PUBLIC UTILITIESSeattle, WA | 1 161 961 served | Purity Score 94 / 100 | |
| 20 | FAIRFAX COUNTY WATER AUTHORITYFairfax County, VA | 1 121 613 served | Purity Score 52 / 100 | |
| 21 | CITY OF AUSTIN WATER & WASTEWATERAustin, TX | 1 115 323 served | Purity Score 72 / 100 | |
| 22 | SUFFOLK COUNTY WATER AUTHORITYSuffolk County, NY | 1 100 000 served | Purity Score 42 / 100 | |
| 23 | ATLANTAAtlanta, GA | 1 089 893 served | Purity Score 91 / 100 | |
| 24 | GWINNETT CO. DEPT. OF WATER RESOURCESGwinnett County, GA | 975 000 served | Purity Score 100 / 100 | |
| 25 | CITY OF FORT WORTHFort Worth, TX | 955 900 served | Purity Score 46 / 100 |
Comparable does not mean complete.
This snapshot compares water systems on one metric. It never replaces a full system report, a city-resolution check, or a certified household test — and missing monitoring is excluded, never scored as favorable.