Chlorate Contamination

Chlorate in Wisconsin Drinking Water

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

Cities Tested

Over HA

33%

% Over HA

242.7 µg/L

State Avg

▼ 26% vs national

vs National

388

Health Violations

Analysis

Chlorate in Wisconsin: what the data shows

Wisconsin has 63 cities with chlorate data from the EPA's UCMR 3 program (2013–2015). Chlorate exceeded the 210 µg/L EPA lifetime health advisory in 21 of those cities. The state average max detected level is 242.7 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)

Wisconsin

33%

21 of 63 cities

← ▼ 26% below national rate (better)

National avg

59%

1866 of 3166 cities

City Map

Chlorate data across Wisconsin

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 Wisconsin

Highest Chlorate levels (µg/L)

All Cities

All Wisconsin cities ranked by chlorate level

#	City	Level	Over HA?	Violations	Grade
1	Green Bay	1755.8 µg/L	Over HA	74	D+
2	Stoughton	1442.8 µg/L	Over HA	4	B+
3	Menasha	869.5 µg/L	Over HA	1	B+
4	Bowler	850.6 µg/L	Over HA	8	A-
5	Weston	707.5 µg/L	Over HA	0	B+
6	Marshfield	580.3 µg/L	Over HA	9	C-
7	Marinette	479.1 µg/L	Over HA	0	A-
8	Two Rivers	361.2 µg/L	Over HA	5	C-
9	Germantown	360.4 µg/L	Over HA	8	B-
10	Wausau	341.2 µg/L	Over HA	24	C
11	Rhinelander	340.0 µg/L	Over HA	5	B
12	Whitewater	330.2 µg/L	Over HA	22	C+
13	Wrightstown	319.9 µg/L	Over HA	4	B
14	Shawano	250.6 µg/L	Over HA	11	A
15	Whitefish Bay	242.0 µg/L	Over HA	0	B+
16	Omro	234.4 µg/L	Over HA	1	A-
17	Glendale	226.0 µg/L	Over HA	1	A-
18	Oak Creek	226.0 µg/L	Over HA	5	B
19	Waukesha	222.1 µg/L	Over HA	320	D
20	Franklin	213.4 µg/L	Over HA	10	B
21	Edgar	211.0 µg/L	Over HA	1	B+
22	Lac Du Flambeau	210.0 µg/L	No	1	A
23	Caledonia	207.4 µg/L	No	1	B
24	Hayward	190.0 µg/L	No	19	F
25	Cedarburg	187.6 µg/L	No	1	B+
26	Fond Du Lac	175.1 µg/L	No	51	F
27	Fort Mccoy	167.5 µg/L	No	4	B+
28	Kaukauna	165.3 µg/L	No	9	B+
29	Neenah	159.5 µg/L	No	6	C+
30	Brown Deer	158.0 µg/L	No	5	A
31	New Berlin	157.1 µg/L	No	14	B
32	Monroe	156.8 µg/L	No	9	A-
33	Fitchburg	155.7 µg/L	No	0	A
34	Grafton	143.5 µg/L	No	12	C+
35	Sheboygan	140.0 µg/L	No	1	A-
36	West Bend	136.9 µg/L	No	11	F
37	Wauwatosa	133.3 µg/L	No	1	B+
38	Manawa	130.7 µg/L	No	2	B
39	Sheboygan Falls	130.0 µg/L	No	5	B-
40	Arlington	128.1 µg/L	No	7	B
41	Kiel	120.0 µg/L	No	3	A-
42	Menomonee Falls	113.1 µg/L	No	6	B+
43	Chippewa Falls	112.8 µg/L	No	12	D+
44	Milwaukee	110.0 µg/L	No	2	A
45	Shorewood	109.7 µg/L	No	1	A-
46	Grand Chute	102.7 µg/L	No	2	A
47	Eau Claire	101.7 µg/L	No	18	D+
48	Little Chute	100.0 µg/L	No	1	B+
49	Waunakee	94.7 µg/L	No	11	B-
50	Brookfield	83.0 µg/L	No	32	C-
51	Fort Atkinson	72.6 µg/L	No	14	A-
52	Portage	67.1 µg/L	No	9	B
53	Hartland	65.7 µg/L	No	8	B
54	West Allis	62.4 µg/L	No	0	A-
55	Greendale	57.3 µg/L	No	1	A-
56	Plover	56.1 µg/L	No	9	B+
57	Wisconsin Rapids	50.1 µg/L	No	6	B-
58	Stevens Point	42.2 µg/L	No	14	C+
59	Superior	40.3 µg/L	No	17	F
60	La Crosse	38.0 µg/L	No	34	F
61	Sun Prairie	37.9 µg/L	No	4	A
62	Madison	29.0 µg/L	No	14	F
63	Cudahy	26.3 µg/L	No	0	B+

FAQ

Frequently asked questions about chlorate in Wisconsin

Is chlorate in Wisconsin tap water dangerous?

Chlorate has no federal MCL. The EPA lifetime health advisory is 210 µg/L. 21 cities in Wisconsin 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 Wisconsin 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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