Chlorate in Hawaii Drinking Water
Ranked by max chlorate detected (µg/L) · UCMR 3 data (2013–2015) · Data from EPA SDWIS & UCMR
Chlorate in Hawaii: what the data shows
Hawaii has 13 cities with chlorate data from the EPA's UCMR 3 program (2013–2015). Chlorate exceeded the 210 µg/L EPA lifetime health advisory in 4 of those cities. The state average max detected level is 149.0 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 Hawaii
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 Hawaii
All Hawaii cities ranked by chlorate level
| # | City | Level | Level | Over HA? | Violations | Grade |
|---|---|---|---|---|---|---|
| 1 | Hawaiian Shores Dho | 310.0 µg/L | Over HA | 2 | A | |
| 2 | Makawao | 270.0 µg/L | Over HA | 83 | B+ | |
| 3 | Wailuku | 220.0 µg/L | Over HA | 3 | A | |
| 4 | Lihue-Kapaa | 220.0 µg/L | Over HA | 0 | A | |
| 5 | Kaanapali (Dho) | 202.0 µg/L | No | 3 | A | |
| 6 | Honolulu-Windward-Pearlharbor | 160.0 µg/L | No | 1 | A | |
| 7 | Schofield Barracks | 140.0 µg/L | No | 3 | A | |
| 8 | Lahaina | 140.0 µg/L | No | 106 | B | |
| 9 | Waipahu-Ewa-Waianae | 95.0 µg/L | No | 0 | A | |
| 10 | Kalaheo | 73.0 µg/L | No | 0 | A- | |
| 11 | Mililani Bws | 46.0 µg/L | No | 0 | A+ | |
| 12 | Pearl Harbor | 39.0 µg/L | No | 2 | A | |
| 13 | Waialua-Haleiwa | 22.0 µg/L | No | 1 | B+ |
Frequently asked questions about chlorate in Hawaii
Is chlorate in Hawaii tap water dangerous?
Chlorate has no federal MCL. The EPA lifetime health advisory is 210 µg/L. 4 cities in Hawaii 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 Hawaii 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.