Chlorate in Maine Drinking Water
Ranked by max chlorate detected (µg/L) · UCMR 3 data (2013–2015) · Data from EPA SDWIS & UCMR
Chlorate in Maine: what the data shows
Maine has 44 cities with chlorate data from the EPA's UCMR 3 program (2013–2015). Chlorate exceeded the 210 µg/L EPA lifetime health advisory in 21 of those cities. The state average max detected level is 238.1 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 Maine
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 Maine
Highest Chlorate levels (µg/L)
All Maine cities ranked by chlorate level
| # | City | Level | Level | Over HA? | Violations | Grade |
|---|---|---|---|---|---|---|
| 1 | Fairfield | 510.0 µg/L | Over HA | 8 | F | |
| 2 | Oakland | 510.0 µg/L | Over HA | 6 | B- | |
| 3 | Vassalboro | 510.0 µg/L | Over HA | 8 | C | |
| 4 | Waterville | 510.0 µg/L | Over HA | 1 | B | |
| 5 | Winslow | 510.0 µg/L | Over HA | 1 | B | |
| 6 | Lewiston | 428.5 µg/L | Over HA | 5 | A- | |
| 7 | Auburn | 396.8 µg/L | Over HA | 8 | B+ | |
| 8 | Topsham | 340.0 µg/L | Over HA | 17 | C+ | |
| 9 | Sanford | 310.0 µg/L | Over HA | 16 | B- | |
| 10 | York | 310.0 µg/L | Over HA | 0 | A+ | |
| 11 | Clifton | 299.4 µg/L | Over HA | 5 | B+ | |
| 12 | Eddington | 299.4 µg/L | Over HA | 5 | B+ | |
| 13 | Orrington | 299.4 µg/L | Over HA | 7 | B | |
| 14 | Brewer | 299.4 µg/L | Over HA | 5 | A- | |
| 15 | Kennebunk | 290.0 µg/L | Over HA | 1 | A | |
| 16 | Kennebunkport | 290.0 µg/L | Over HA | 1 | A | |
| 17 | Bangor | 260.0 µg/L | Over HA | 3 | B | |
| 18 | Hermon | 260.0 µg/L | Over HA | 5 | C+ | |
| 19 | Veazie | 260.0 µg/L | Over HA | 1 | B+ | |
| 20 | Hampden | 260.0 µg/L | Over HA | 2 | B+ | |
| 21 | Wilton | 240.0 µg/L | Over HA | 0 | B+ | |
| 22 | Kittery | 201.0 µg/L | No | 1 | A | |
| 23 | Camden | 160.0 µg/L | No | 11 | B | |
| 24 | Rockland | 160.0 µg/L | No | 4 | A- | |
| 25 | Rockport | 160.0 µg/L | No | 9 | B- | |
| 26 | Thomaston | 160.0 µg/L | No | 4 | A- | |
| 27 | Warren | 160.0 µg/L | No | 4 | A- | |
| 28 | Cape Elizabeth | 140.0 µg/L | No | 0 | A | |
| 29 | Cumberland | 140.0 µg/L | No | 0 | A | |
| 30 | Falmouth | 140.0 µg/L | No | 0 | A | |
| 31 | Portland | 140.0 µg/L | No | 0 | A | |
| 32 | Raymond | 140.0 µg/L | No | 12 | C- | |
| 33 | Scarborough | 140.0 µg/L | No | 26 | C | |
| 34 | South Portland | 140.0 µg/L | No | 0 | A | |
| 35 | Westbrook | 140.0 µg/L | No | 0 | A | |
| 36 | Windham | 140.0 µg/L | No | 5 | B- | |
| 37 | Gorham | 140.0 µg/L | No | 7 | B | |
| 38 | Biddeford | 120.0 µg/L | No | 1 | A | |
| 39 | Saco | 120.0 µg/L | No | 1 | A | |
| 40 | Augusta | 95.0 µg/L | No | 8 | B+ | |
| 41 | Chelsea | 95.0 µg/L | No | 1 | A- | |
| 42 | Manchester | 95.0 µg/L | No | 7 | B+ | |
| 43 | Winthrop | 95.0 µg/L | No | 15 | B+ | |
| 44 | Old Town | 61.0 µg/L | No | 1 | A- |
Frequently asked questions about chlorate in Maine
Is chlorate in Maine tap water dangerous?
Chlorate has no federal MCL. The EPA lifetime health advisory is 210 µg/L. 21 cities in Maine 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 Maine 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.