Chlorate Contamination

Chlorate in Illinois Drinking Water

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

103

Cities Tested

Over HA

41%

% Over HA

344.1 µg/L

State Avg

▼ 17% vs national

vs National

687

Health Violations

Analysis

Chlorate in Illinois: what the data shows

Illinois has 103 cities with chlorate data from the EPA's UCMR 3 program (2013–2015). Chlorate exceeded the 210 µg/L EPA lifetime health advisory in 42 of those cities. The state average max detected level is 344.1 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)

Illinois

41%

42 of 103 cities

← ▼ 17% below national rate (better)

National avg

58%

1812 of 3098 cities

City Map

Chlorate data across Illinois

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 Illinois

Highest Chlorate levels (µg/L)

All Cities

All Illinois cities ranked by chlorate level

#	City	Level	Over HA?	Violations	Grade
1	Lindenhurst	4620.0 µg/L	Over HA	0	B+
2	Freeburg	2796.9 µg/L	Over HA	7	A-
3	Atkinson	2410.0 µg/L	Over HA	3	B+
4	Charleston	1240.9 µg/L	Over HA	10	C+
5	Pontiac	1160.0 µg/L	Over HA	10	C
6	Lake Bluff	964.0 µg/L	Over HA	18	C+
7	Algonquin	814.6 µg/L	Over HA	6	A-
8	Shorewood	810.0 µg/L	Over HA	4	A-
9	Carterville	809.7 µg/L	Over HA	3	C+
10	Marion	759.1 µg/L	Over HA	29	D
11	Chatham	741.9 µg/L	Over HA	2	A
12	Tamaroa	672.9 µg/L	Over HA	0	A-
13	Mount Vernon	650.0 µg/L	Over HA	2	B+
14	Gifford	644.0 µg/L	Over HA	0	B
15	Streator	640.0 µg/L	Over HA	14	A-
16	Good Hope	592.3 µg/L	Over HA	4	A-
17	Mchenry	567.2 µg/L	Over HA	57	F
18	Champaign	560.0 µg/L	Over HA	0	A
19	Dieterich	546.8 µg/L	Over HA	7	F
20	Freeport	543.0 µg/L	Over HA	19	B-
21	Moline	516.6 µg/L	Over HA	7	C
22	Joliet	500.0 µg/L	Over HA	131	F
23	Machesney Park	466.1 µg/L	Over HA	4	B
24	Peoria	460.0 µg/L	Over HA	5	C-
25	Benton	426.7 µg/L	Over HA	5	D
26	North Pekin	409.0 µg/L	Over HA	1	A-
27	Aurora	360.0 µg/L	Over HA	20	D
28	Jerseyville	346.8 µg/L	Over HA	6	A-
29	Kankakee	340.0 µg/L	Over HA	40	F
30	Murphysboro	340.0 µg/L	Over HA	8	B
31	East Moline	339.5 µg/L	Over HA	18	D+
32	Plano	312.8 µg/L	Over HA	0	B+
33	West Chicago	310.0 µg/L	Over HA	22	A
34	Alton	300.0 µg/L	Over HA	1	B
35	Herrin	292.1 µg/L	Over HA	0	C+
36	Nashville	290.0 µg/L	Over HA	27	C-
37	Western Springs	280.0 µg/L	Over HA	2	B
38	Crystal Lake	270.0 µg/L	Over HA	4	A-
39	O Fallon	250.0 µg/L	Over HA	17	A-
40	Park Forest	220.0 µg/L	Over HA	2	A
41	Belvidere	219.2 µg/L	Over HA	8	A-
42	Country Club Hills	211.8 µg/L	Over HA	0	A-
43	Saint Charles	210.0 µg/L	No	3	B+
44	Batavia	210.0 µg/L	No	33	B+
45	Granite City	200.0 µg/L	No	0	B+
46	Westmont	190.0 µg/L	No	6	B-
47	North Aurora	190.0 µg/L	No	27	A-
48	Decatur	178.8 µg/L	No	28	B
49	Edwardsville	175.3 µg/L	No	18	D+
50	East St Louis	170.0 µg/L	No	1	B+
51	Northbrook	150.0 µg/L	No	55	D
52	Justice	149.4 µg/L	No	0	A-
53	Normal	147.4 µg/L	No	3	D+
54	Grays Lake	144.7 µg/L	No	6	A
55	Round Lake	140.0 µg/L	No	3	A-
56	Mundelein	136.9 µg/L	No	22	F
57	Lake Forest	135.8 µg/L	No	58	B-
58	Quincy	124.0 µg/L	No	3	B-
59	Gurnee	120.0 µg/L	No	4	A
60	Bridgeview	119.2 µg/L	No	0	A-
61	Hazel Crest	112.7 µg/L	No	2	B
62	Round Lake Beach	111.3 µg/L	No	3	B+
63	Godfrey	110.0 µg/L	No	22	C+
64	Libertyville	110.0 µg/L	No	14	C
65	Glenview	110.0 µg/L	No	3	B+
66	Geneva	110.0 µg/L	No	67	B-
67	Wilmette	110.0 µg/L	No	0	A
68	River Forest	110.0 µg/L	No	1	B+
69	Pekin	100.0 µg/L	No	1	D+
70	Rock Island	94.0 µg/L	No	5	B-
71	Highland Park	89.0 µg/L	No	2	B+
72	La Grange Park	85.7 µg/L	No	2	A
73	East Peoria	85.2 µg/L	No	133	F
74	Rockford	79.9 µg/L	No	43	F
75	Collinsville	73.0 µg/L	No	12	C-
76	Orion	72.8 µg/L	No	2	B-
77	Caseyville	66.0 µg/L	No	3	B+
78	Hickory Hills	63.0 µg/L	No	1	A
79	Lombard	62.0 µg/L	No	1	A-
80	Carbondale	53.2 µg/L	No	26	D
81	Taylorville	48.0 µg/L	No	0	A-
82	Bolingbrook	46.0 µg/L	No	2	A
83	Niles	46.0 µg/L	No	3	B
84	Wheeling	45.3 µg/L	No	5	A+
85	Buffalo Grove	43.1 µg/L	No	1	A
86	Crestwood	42.8 µg/L	No	0	B
87	Arlington Heights	37.3 µg/L	No	1	B-
88	Palatine	37.0 µg/L	No	2	B
89	Effingham	36.0 µg/L	No	2	A-
90	Morton Grove	34.0 µg/L	No	2	B-
91	Alsip	33.0 µg/L	No	2	A-
92	Rolling Meadows	32.0 µg/L	No	3	A
93	Naperville	30.0 µg/L	No	0	B+
94	Lisle	28.0 µg/L	No	2	A-
95	Elgin	26.0 µg/L	No	9	C-
96	Woodridge	25.0 µg/L	No	2	A-
97	Palos Heights	25.0 µg/L	No	1	A-
98	Elk Grove	24.0 µg/L	No	2	A-
99	Brookfield	22.0 µg/L	No	0	A-
100	Ottawa	21.3 µg/L	No	62	F
101	Mount Prospect	21.0 µg/L	No	1	B+
102	Coleta	21.0 µg/L	No	1	A-
103	Minooka	20.0 µg/L	No	6	A-

FAQ

Frequently asked questions about chlorate in Illinois

Is chlorate in Illinois tap water dangerous?

Chlorate has no federal MCL. The EPA lifetime health advisory is 210 µg/L. 42 cities in Illinois 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 Illinois 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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