Chlorate in Colorado Drinking Water
Ranked by max chlorate detected (µg/L) · UCMR 3 data (2013–2015) · Data from EPA SDWIS & UCMR
Chlorate in Colorado: what the data shows
Colorado has 54 cities with chlorate data from the EPA's UCMR 3 program (2013–2015). Chlorate exceeded the 210 µg/L EPA lifetime health advisory in 25 of those cities. The state average max detected level is 409.1 µg/L. Chlorate is a disinfection byproduct that forms when chlorine dioxide or hypochlorite solutions are used to disinfect drinking water. It is most common in systems that use chlorine dioxide for taste-and-odor control or that store hypochlorite for extended periods. There is no federal MCL — the EPA lifetime health advisory is 210 µg/L. Chlorate can interfere with thyroid function by blocking iodide uptake, an effect of particular concern for pregnant women, infants, and people with thyroid conditions. Reverse osmosis and ion exchange (anion-specific) are effective at removing chlorate; standard activated carbon filters provide only modest reduction.
Cities exceeding 210 µg/L EPA lifetime HA (no MCL)
Chlorate data across Colorado
Each dot is a city with UCMR 3 chlorate testing data. Cities where chlorate exceeds the 210 µg/L EPA lifetime health advisory are highlighted. Size reflects population served.
Top 10 cities by chlorate level in Colorado
Highest Chlorate levels (µg/L)
All Colorado cities ranked by chlorate level
| # | City | Level | Level | Over HA? | Violations | Grade |
|---|---|---|---|---|---|---|
| 1 | Arvada | 2400.0 µg/L | Over HA | 1 | B+ | |
| 2 | Vail | 1700.0 µg/L | Over HA | 0 | A | |
| 3 | Superior | 1700.0 µg/L | Over HA | 5 | A | |
| 4 | Aurora | 1200.0 µg/L | Over HA | 22 | F | |
| 5 | Colorado Springs | 1200.0 µg/L | Over HA | 117 | F | |
| 6 | Thornton | 1100.0 µg/L | Over HA | 3 | F | |
| 7 | Monument | 990.0 µg/L | Over HA | 23 | F | |
| 8 | Brighton | 940.0 µg/L | Over HA | 18 | F | |
| 9 | Englewood | 800.0 µg/L | Over HA | 33 | D | |
| 10 | Highlands Ranch | 720.0 µg/L | Over HA | 0 | B- | |
| 11 | Castle Rock | 660.0 µg/L | Over HA | 20 | F | |
| 12 | Parker | 640.0 µg/L | Over HA | 4 | F | |
| 13 | Centennial | 620.0 µg/L | Over HA | 18 | F | |
| 14 | Lakewood | 510.0 µg/L | Over HA | 28 | F | |
| 15 | Pueblo | 460.0 µg/L | Over HA | 15 | F | |
| 16 | Broomfield | 400.0 µg/L | Over HA | 5 | B | |
| 17 | Westminster | 350.0 µg/L | Over HA | 1 | D | |
| 18 | Estes Park | 340.0 µg/L | Over HA | 49 | D | |
| 19 | Dolores | 340.0 µg/L | Over HA | 1 | B | |
| 20 | Florence | 340.0 µg/L | Over HA | 2 | C+ | |
| 21 | Federal Heights | 330.0 µg/L | Over HA | 0 | B+ | |
| 22 | Palmer Lake | 300.0 µg/L | Over HA | 15 | D | |
| 23 | Pueblo West | 299.0 µg/L | Over HA | 5 | B- | |
| 24 | Erie | 275.0 µg/L | Over HA | 1 | A | |
| 25 | Boulder | 250.0 µg/L | Over HA | 15 | F | |
| 26 | Empire | 210.0 µg/L | No | 14 | C+ | |
| 27 | Wellington | 203.0 µg/L | No | 4 | B- | |
| 28 | Grand Junction | 195.3 µg/L | No | 4 | B | |
| 29 | Golden | 190.0 µg/L | No | 18 | B- | |
| 30 | Northglenn | 184.0 µg/L | No | 0 | A+ | |
| 31 | Sterling | 180.0 µg/L | No | 29 | C- | |
| 32 | Commerce City | 160.0 µg/L | No | 0 | A | |
| 33 | Canon City | 150.0 µg/L | No | 4 | B+ | |
| 34 | Longmont | 140.0 µg/L | No | 2 | A- | |
| 35 | Aspen | 130.0 µg/L | No | 2 | D | |
| 36 | Lafayette | 120.0 µg/L | No | 19 | F | |
| 37 | Greeley | 110.0 µg/L | No | 16 | F | |
| 38 | Steamboat Springs | 110.0 µg/L | No | 57 | F | |
| 39 | Fountain | 100.0 µg/L | No | 4 | F | |
| 40 | Evans | 100.0 µg/L | No | 0 | B+ | |
| 41 | Pagosa Springs | 99.0 µg/L | No | 25 | F | |
| 42 | Niwot | 91.0 µg/L | No | 1 | A | |
| 43 | Windsor | 87.0 µg/L | No | 51 | D | |
| 44 | Louisville | 85.1 µg/L | No | 2 | A- | |
| 45 | Eaton | 77.5 µg/L | No | 1 | B- | |
| 46 | Berthoud | 71.0 µg/L | No | 8 | C+ | |
| 47 | Lucerne | 71.0 µg/L | No | 0 | B+ | |
| 48 | Fort Collins | 67.0 µg/L | No | 6 | D | |
| 49 | Fort Morgan | 67.0 µg/L | No | 5 | A- | |
| 50 | Gunnison | 53.0 µg/L | No | 14 | C | |
| 51 | Usaf Academy | 52.2 µg/L | No | 3 | A | |
| 52 | Loveland | 50.9 µg/L | No | 50 | F | |
| 53 | Crestone | 41.9 µg/L | No | 2 | B- | |
| 54 | Durango | 33.9 µg/L | No | 112 | F |
Frequently asked questions about chlorate in Colorado
Is chlorate in Colorado tap water dangerous?
Chlorate has no federal MCL. The EPA lifetime health advisory is 210 µg/L. 25 cities in Colorado exceed this level. Chlorate can interfere with thyroid iodide uptake, which is a particular concern for infants, pregnant women, and people with hypothyroidism.
Where does chlorate in Colorado water come from?
Chlorate is a byproduct of chlorine-based disinfectants — particularly chlorine dioxide and hypochlorite (bleach) solutions. Levels tend to be higher in systems that use chlorine dioxide for taste-and-odor treatment or store sodium hypochlorite at high concentrations or for long periods. Levels vary seasonally with disinfectant use.
How can I reduce chlorate exposure?
Reverse osmosis is the most effective home treatment for chlorate, typically removing 80–95%. Anion exchange systems also work but require regeneration. Standard activated carbon filters provide only limited chlorate reduction. Boiling does NOT remove chlorate.