Colorado Water Quality Rankings 2026: Best & Worst Cities

This page ranks the 35 Colorado cities whose water systems we have matched to EPA records. Every city starts at 100 points and loses points for health-based EPA violations in the last five years (SDWIS 2026Q2), its most recent Lead and Copper Rule 90th-percentile result, PFAS detected in EPA's 2023–2026 UCMR5 monitoring, and 2012–2019 compliance samples that averaged near or above a limit. Letters follow fixed bands (A ≥90, B ≥80, C ≥70, D ≥60, F below 60). Cities run from the highest score (Pueblo) down to the lowest (Brighton); ties are ordered by population served. See the full scoring methodology for every deduction and the data vintages.

What your city's grade means

An A or B grade points to water that consistently tests within federal safety limits, while a C suggests moderate issues worth watching and a D or F flags contaminants or compliance problems serious enough to act on. These grades describe system-level water leaving the treatment plant — they can't account for your home's own plumbing, so older houses with lead service lines or fixtures can add contaminants after the water arrives. For a contaminant-by-contaminant view, see the Colorado contaminant breakdown or drill into the county-level rankings.

What Colorado residents should do

• Find your city in the ranking below and open its full report for its violation history, lead results and PFAS table.
• See how Colorado compares against the best-rated and worst-rated cities nationwide.
• Test your home's water if you have concerns — the most common issues involve lead, PFAS, and arsenic.
• Check whether your utility still has lead service lines in Colorado — EPA's inventory counts lead pipes by water system, a risk that plant-level grades cannot capture. Read the lead guide for testing and filter options.
• If treatment makes sense for your situation, compare certified water filters matched to the contaminants found in your area.

We track 35 cities in Colorado. 35 of them are matched to an active EPA-registered community water system (PWSID). Those 35 systems report serving 4,742,845 people in EPA's Safe Drinking Water Information System (SDWIS).

Of all 35 cities Colorado cities we can grade from EPA records, 31 cities (89%) grade B or better, 2 sit in the C range and 2 grade D or F. The average score is 94/100.

EPA records 2 health-based violations in the last five years across 2 cities. Monitoring and reporting violations (93 in the same window) are paperwork lapses and cost far fewer points.

31 cities have a Lead and Copper Rule 90th-percentile result from 2020 or later: 4 cities at 5 ppb or more.

EPA's UCMR5 PFAS monitoring (2023–2026) covers 32 cities: PFAS were detected in 9 cities, and PFOA or PFOS reached EPA's 4 ppt limit in 4 cities.

Centennial scores highest (100) and Brighton lowest (64), a 36-point spread.

Lead pipes are the part of tap-water risk a treatment-plant grade cannot see, so start with EPA's service line inventory (Q2 2026 snapshot). 1,234 Colorado systems inventoried 1,826,911 service lines: 18,792 confirmed lead plus 2,620 galvanized lines requiring replacement, spread across 21 systems. Only 141,309 lines (7.7%) remain unverified, so Colorado's inventory is comparatively complete.

Of the 32 city-linked Colorado utilities with an inventory on file, 13 report at least one lead or galvanized-requiring-replacement line, 1 reports none but still has a quarter or more of its lines unverified, and 18 report no lead with most lines verified. DENVER WATER BOARD, which serves Denver and 1,287,000 people, is the biggest and reports 15,826 lead lines and 848 galvanized requiring replacement.

Colorado's guide on this site singles out uranium and radium, selenium, nitrates, and disinfection byproducts. Uranium (EPA MCL 30 µg/L) increases cancer risk and is toxic to the kidneys; Selenium (EPA MCL 0.05 mg/L) can cause hair and fingernail loss, numbness and circulatory problems; Nitrate (EPA MCL 10 mg/L (as nitrogen)) can cause methemoglobinemia ("blue baby syndrome") in infants under six months; Disinfection byproducts (regulated as TTHM (80 ppb) and HAA5 (60 ppb)) are associated with increased cancer risk over long exposure.

Where a system draws its water shapes which of these show up. Disinfection byproducts are a surface-water signature: chlorine reacts with organic matter in rivers and reservoirs, so byproducts tend to run higher where systems chlorinate surface water. Uranium and selenium are naturally occurring and tend to show up in groundwater, leaching from bedrock into aquifers rather than arriving from pollution. Nitrate follows fertilizer, manure and septic loading, so it is most often a concern for systems drawing shallow groundwater in farm regions. Lead is different again: it enters after treatment from service lines and household plumbing, which is why the inventory figures above matter more than plant-level results. Your utility's Consumer Confidence Report names your source.

The best water quality in Colorado is found in Pueblo with a score of 100/100 and a grade of A. This puts Pueblo among the top-performing cities in the country for drinking water safety.

The most concerning water quality is in Brighton scoring 64/100 with a grade of D. Residents may want to consider home water testing and filtration options.

The statewide average score is 94/100, which is 6 points above the national average of 88/100. A strong majority (86%) of Colorado cities exceed the national average, indicating generally good water infrastructure across the state.