Chlorate in Arizona Drinking Water
Ranked by max chlorate detected (µg/L) · UCMR 3 data (2013–2015) · Data from EPA SDWIS & UCMR
Chlorate in Arizona: what the data shows
Arizona has 56 cities with chlorate data from the EPA's UCMR 3 program (2013–2015). Chlorate exceeded the 210 µg/L EPA lifetime health advisory in 31 of those cities. The state average max detected level is 353.5 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 Arizona
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 Arizona
Highest Chlorate levels (µg/L)
All Arizona cities ranked by chlorate level
| # | City | Level | Level | Over HA? | Violations | Grade |
|---|---|---|---|---|---|---|
| 1 | Yuma | 1700.0 µg/L | Over HA | 318 | F | |
| 2 | Green Valley | 1500.0 µg/L | Over HA | 9 | D | |
| 3 | Buckeye | 1200.0 µg/L | Over HA | 103 | F | |
| 4 | Tucson | 1100.0 µg/L | Over HA | 150 | F | |
| 5 | Mohave Valley | 1000.0 µg/L | Over HA | 14 | F | |
| 6 | Phoenix | 884.0 µg/L | Over HA | 59 | F | |
| 7 | Litchfield Park | 780.0 µg/L | Over HA | 21 | F | |
| 8 | Payson | 720.0 µg/L | Over HA | 60 | F | |
| 9 | Catalina | 710.0 µg/L | Over HA | 2 | D | |
| 10 | Whiteriver | 590.0 µg/L | Over HA | 7 | D | |
| 11 | Somerton | 540.0 µg/L | Over HA | 17 | D | |
| 12 | Fountain Hills | 530.0 µg/L | Over HA | 21 | F | |
| 13 | Tempe | 480.0 µg/L | Over HA | 3 | D+ | |
| 14 | Apache Junction | 450.0 µg/L | Over HA | 18 | F | |
| 15 | Mesa | 440.0 µg/L | Over HA | 3 | F | |
| 16 | Surprise | 400.0 µg/L | Over HA | 18 | F | |
| 17 | Heber | 400.0 µg/L | Over HA | 11 | F | |
| 18 | Vaya Chin, Hickiwan, San Simon Village/S | 360.0 µg/L | Over HA | 1 | A- | |
| 19 | Scottsdale | 320.0 µg/L | Over HA | 22 | F | |
| 20 | Cave Creek | 320.0 µg/L | Over HA | 25 | C- | |
| 21 | Sedona | 320.0 µg/L | Over HA | 174 | F | |
| 22 | Chandler | 310.0 µg/L | Over HA | 32 | F | |
| 23 | Avondale | 310.0 µg/L | Over HA | 13 | C+ | |
| 24 | El Mirage | 310.0 µg/L | Over HA | 3 | D | |
| 25 | Sacaton, Sacaton Flats,Upper San Tan, Bl | 310.0 µg/L | Over HA | 11 | B | |
| 26 | Goodyear | 290.0 µg/L | Over HA | 3 | F | |
| 27 | Maricopa | 280.0 µg/L | Over HA | 228 | D | |
| 28 | Sun City West | 270.0 µg/L | Over HA | 3 | B+ | |
| 29 | Florence | 270.0 µg/L | Over HA | 60 | F | |
| 30 | Red Rock | 222.0 µg/L | Over HA | 1 | D+ | |
| 31 | Sierra Vista | 220.0 µg/L | Over HA | 44 | D | |
| 32 | Paradise Valley | 200.0 µg/L | No | 3 | C | |
| 33 | Nogales | 170.0 µg/L | No | 39 | F | |
| 34 | Anthem | 160.0 µg/L | No | 1 | B | |
| 35 | Glendale | 150.0 µg/L | No | 5 | F | |
| 36 | Oro Valley | 140.0 µg/L | No | 11 | D | |
| 37 | Cottonwood | 130.0 µg/L | No | 184 | D | |
| 38 | Show Low | 130.0 µg/L | No | 60 | D | |
| 39 | Kingman | 120.0 µg/L | No | 110 | D | |
| 40 | Bullhead City | 120.0 µg/L | No | 57 | F | |
| 41 | Upper Fruitland, Nenahnezad, San Juan, N | 110.0 µg/L | No | 9 | B+ | |
| 42 | Upper Fruitland, Nenahnezad, San Juan, N | 110.0 µg/L | No | 9 | B+ | |
| 43 | Gilbert | 100.0 µg/L | No | 11 | F | |
| 44 | Globe | 88.0 µg/L | No | 46 | F | |
| 45 | San Luis | 74.0 µg/L | No | 8 | D | |
| 46 | Buckeye-Sono | 73.0 µg/L | No | 2 | B- | |
| 47 | Holbrook | 71.7 µg/L | No | 6 | F | |
| 48 | Flagstaff | 54.0 µg/L | No | 74 | D | |
| 49 | Fort Defiance, Window Rock, St. Michaels | 49.0 µg/L | No | 22 | B- | |
| 50 | Fort Huachuca | 46.0 µg/L | No | 9 | F | |
| 51 | Sun City | 35.0 µg/L | No | 1 | B | |
| 52 | Johnson Ranch | 34.0 µg/L | No | 7 | D | |
| 53 | Prescott | 30.0 µg/L | No | 33 | F | |
| 54 | Sahuarita | 25.0 µg/L | No | 19 | F | |
| 55 | Benson | 23.0 µg/L | No | 29 | D | |
| 56 | Peoria | 20.0 µg/L | No | 13 | F |
Frequently asked questions about chlorate in Arizona
Is chlorate in Arizona tap water dangerous?
Chlorate has no federal MCL. The EPA lifetime health advisory is 210 µg/L. 31 cities in Arizona 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 Arizona 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.