Chlorate in Maryland Drinking Water
Ranked by max chlorate detected (µg/L) · UCMR 3 data (2013–2015) · Data from EPA SDWIS & UCMR
Chlorate in Maryland: what the data shows
Maryland has 22 cities with chlorate data from the EPA's UCMR 3 program (2013–2015). Chlorate exceeded the 210 µg/L EPA lifetime health advisory in 13 of those cities. The state average max detected level is 432.5 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 Maryland
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 Maryland
Highest Chlorate levels (µg/L)
All Maryland cities ranked by chlorate level
| # | City | Level | Level | Over HA? | Violations | Grade |
|---|---|---|---|---|---|---|
| 1 | Snow Hill | 2000.0 µg/L | Over HA | 4 | B+ | |
| 2 | Patuxent River | 994.0 µg/L | Over HA | 2 | A- | |
| 3 | Elkton | 828.0 µg/L | Over HA | 42 | F | |
| 4 | Westminster | 698.0 µg/L | Over HA | 29 | F | |
| 5 | Aberdeen | 611.0 µg/L | Over HA | 0 | B | |
| 6 | Millersville | 590.0 µg/L | Over HA | 13 | F | |
| 7 | Berlin | 550.0 µg/L | Over HA | 6 | D | |
| 8 | Frederick | 530.0 µg/L | Over HA | 18 | F | |
| 9 | Abingdon | 433.5 µg/L | Over HA | 0 | A | |
| 10 | Prince Frederick | 429.1 µg/L | Over HA | 4 | B | |
| 11 | Fort Meade | 300.0 µg/L | Over HA | 3 | A | |
| 12 | Baltimore | 233.0 µg/L | Over HA | 12 | F | |
| 13 | Annapolis | 232.0 µg/L | Over HA | 3 | A- | |
| 14 | California | 200.0 µg/L | No | 2 | C- | |
| 15 | Columbia | 198.0 µg/L | No | 50 | C+ | |
| 16 | Hagerstown | 192.0 µg/L | No | 42 | C | |
| 17 | Ocean City | 137.0 µg/L | No | 15 | C- | |
| 18 | La Plata | 115.0 µg/L | No | 10 | F | |
| 19 | Easton | 98.0 µg/L | No | 6 | A- | |
| 20 | Havre De Grace | 55.1 µg/L | No | 13 | C | |
| 21 | Bowie | 46.2 µg/L | No | 1 | B+ | |
| 22 | Laurel | 46.0 µg/L | No | 0 | A+ |
Frequently asked questions about chlorate in Maryland
Is chlorate in Maryland tap water dangerous?
Chlorate has no federal MCL. The EPA lifetime health advisory is 210 µg/L. 13 cities in Maryland 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 Maryland 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.