Chlorate in Delaware Drinking Water
Ranked by max chlorate detected (µg/L) · UCMR 3 data (2013–2015) · Data from EPA SDWIS & UCMR
Chlorate in Delaware: what the data shows
Delaware has 11 cities with chlorate data from the EPA's UCMR 3 program (2013–2015). Chlorate exceeded the 210 µg/L EPA lifetime health advisory in 5 of those cities. The state average max detected level is 273.4 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 Delaware
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 Delaware
Highest Chlorate levels (µg/L)
All Delaware cities ranked by chlorate level
| # | City | Level | Level | Over HA? | Violations | Grade |
|---|---|---|---|---|---|---|
| 1 | Dover | 660.0 µg/L | Over HA | 35 | B | |
| 2 | Wilmington | 600.0 µg/L | Over HA | 8 | B | |
| 3 | Camden-Wyoming | 380.0 µg/L | Over HA | 35 | B | |
| 4 | New Castle | 279.0 µg/L | Over HA | 9 | B- | |
| 5 | Lewes | 250.0 µg/L | Over HA | 20 | D+ | |
| 6 | Rehoboth Beach | 210.0 µg/L | No | 8 | B | |
| 7 | Bear | 170.0 µg/L | No | 3 | B | |
| 8 | Bear | 170.0 µg/L | No | 3 | B | |
| 9 | Newark | 129.0 µg/L | No | 5 | C- | |
| 10 | Middletown | 86.0 µg/L | No | 17 | B+ | |
| 11 | Bethany Beach | 73.0 µg/L | No | 5 | B+ |
Frequently asked questions about chlorate in Delaware
Is chlorate in Delaware tap water dangerous?
Chlorate has no federal MCL. The EPA lifetime health advisory is 210 µg/L. 5 cities in Delaware 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 Delaware 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.