Chlorate Contamination

Chlorate in Iowa Drinking Water

Ranked by max chlorate detected (µg/L) · UCMR 3 data (2013–2015) · Data from EPA SDWIS & UCMR

Cities Tested

Over HA

61%

% Over HA

452.9 µg/L

State Avg

▲ 2% vs national

vs National

303

Health Violations

Analysis

Chlorate in Iowa: what the data shows

Iowa has 36 cities with chlorate data from the EPA's UCMR 3 program (2013–2015). Chlorate exceeded the 210 µg/L EPA lifetime health advisory in 22 of those cities. The state average max detected level is 452.9 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.

Comparison

Cities exceeding 210 µg/L EPA lifetime HA (no MCL)

Iowa

61%

22 of 36 cities

→ ▲ 2% above national rate (worse)

National avg

59%

1866 of 3166 cities

City Map

Chlorate data across Iowa

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.

Worst Offenders

Top 10 cities by chlorate level in Iowa

Highest Chlorate levels (µg/L)

All Cities

All Iowa cities ranked by chlorate level

#	City	Level	Over HA?	Violations	Grade
1	Scranton	2900.0 µg/L	Over HA	6	B
2	Clinton	2190.0 µg/L	Over HA	0	A-
3	Sioux City	1130.0 µg/L	Over HA	14	B
4	Cedar Falls	932.0 µg/L	Over HA	4	A-
5	Altoona	908.0 µg/L	Over HA	20	B+
6	Waterloo	670.9 µg/L	Over HA	3	A-
7	Ottumwa	639.0 µg/L	Over HA	6	B+
8	Indianola	599.0 µg/L	Over HA	7	A-
9	Fort Madison	550.0 µg/L	Over HA	6	A-
10	Gilbert	456.0 µg/L	Over HA	1	B+
11	Newton	376.3 µg/L	Over HA	2	A
12	Creston	376.0 µg/L	Over HA	9	A-
13	Clive	330.0 µg/L	Over HA	1	A
14	Keokuk	314.0 µg/L	Over HA	0	A-
15	Des Moines	313.0 µg/L	Over HA	7	B+
16	Urbandale	299.0 µg/L	Over HA	0	B+
17	West Des Moines	290.0 µg/L	Over HA	1	B+
18	Ankeny	288.0 µg/L	Over HA	15	B
19	Waverly	288.0 µg/L	Over HA	2	B+
20	Storm Lake	281.0 µg/L	Over HA	1	A-
21	Elk Horn	280.0 µg/L	Over HA	0	B+
22	Mason City	244.0 µg/L	Over HA	18	A-
23	Dubuque	205.0 µg/L	No	30	F
24	Marshalltown	187.0 µg/L	No	4	A-
25	Centerville	169.0 µg/L	No	4	B+
26	Princeton	146.0 µg/L	No	18	B
27	Johnston	140.0 µg/L	No	6	B+
28	Lenox	140.0 µg/L	No	0	A
29	Council Bluffs	135.0 µg/L	No	8	B+
30	Denison	111.0 µg/L	No	0	A
31	Ames	110.0 µg/L	No	15	B+
32	Durant	100.0 µg/L	No	2	A
33	Coralville	87.0 µg/L	No	15	B
34	Iowa City	62.0 µg/L	No	171	F
35	Emmetsburg	38.3 µg/L	No	1	A-
36	Carroll	21.0 µg/L	No	0	B

FAQ

Frequently asked questions about chlorate in Iowa

Is chlorate in Iowa tap water dangerous?

Chlorate has no federal MCL. The EPA lifetime health advisory is 210 µg/L. 22 cities in Iowa 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 Iowa 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.

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