Chlorate in Rhode Island Drinking Water
Ranked by max chlorate detected (µg/L) · UCMR 3 data (2013–2015) · Data from EPA SDWIS & UCMR
Chlorate in Rhode Island: what the data shows
Rhode Island has 18 cities with chlorate data from the EPA's UCMR 3 program (2013–2015). Chlorate exceeded the 210 µg/L EPA lifetime health advisory in 7 of those cities. The state average max detected level is 253.5 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 Rhode Island
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 Rhode Island
Highest Chlorate levels (µg/L)
All Rhode Island cities ranked by chlorate level
| # | City | Level | Level | Over HA? | Violations | Grade |
|---|---|---|---|---|---|---|
| 1 | Middletown | 650.0 µg/L | Over HA | 36 | F | |
| 2 | Middletown | 650.0 µg/L | Over HA | 31 | B | |
| 3 | Middletown | 650.0 µg/L | Over HA | 17 | B | |
| 4 | Cumberland | 450.0 µg/L | Over HA | 11 | B | |
| 5 | Cumberland | 450.0 µg/L | Over HA | 4 | A- | |
| 6 | Cumberland | 450.0 µg/L | Over HA | 4 | A- | |
| 7 | Coventry | 220.0 µg/L | Over HA | 12 | B+ | |
| 8 | Cranston | 110.0 µg/L | No | 4 | B- | |
| 9 | Coventry | 110.0 µg/L | No | 1 | C+ | |
| 10 | Coventry | 110.0 µg/L | No | 7 | F | |
| 11 | Coventry | 110.0 µg/L | No | 6 | C+ | |
| 12 | Coventry | 110.0 µg/L | No | 5 | B | |
| 13 | Coventry | 110.0 µg/L | No | 1 | B+ | |
| 14 | Coventry | 110.0 µg/L | No | 1 | B+ | |
| 15 | Woonsocket | 83.7 µg/L | No | 7 | B- | |
| 16 | Westerly | 82.0 µg/L | No | 5 | C | |
| 17 | South Kingstown | 77.0 µg/L | No | 38 | F | |
| 18 | East Providence | 30.0 µg/L | No | 7 | A- |
Frequently asked questions about chlorate in Rhode Island
Is chlorate in Rhode Island tap water dangerous?
Chlorate has no federal MCL. The EPA lifetime health advisory is 210 µg/L. 7 cities in Rhode Island 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 Rhode Island 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.