Chlorate Contamination

Chlorate in Illinois Drinking Water

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

105

Cities Tested

Over HA

41%

% Over HA

340.4 µg/L

State Avg

▼ 18% vs national

vs National

695

Health Violations

Analysis

Chlorate in Illinois: what the data shows

Illinois has 105 cities with chlorate data from the EPA's UCMR 3 program (2013–2015). Chlorate exceeded the 210 µg/L EPA lifetime health advisory in 43 of those cities. The state average max detected level is 340.4 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.

Comparison

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

Illinois

41%

43 of 105 cities

← ▼ 18% below national rate (better)

National avg

59%

1866 of 3166 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	D+
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	Vernon Hills	270.0 µg/L	Over HA	4	B+
40	O Fallon	250.0 µg/L	Over HA	17	A-
41	Park Forest	220.0 µg/L	Over HA	2	A
42	Belvidere	219.2 µg/L	Over HA	8	A-
43	Country Club Hills	211.8 µg/L	Over HA	0	A-
44	Saint Charles	210.0 µg/L	No	3	B+
45	Batavia	210.0 µg/L	No	33	B+
46	Granite City	200.0 µg/L	No	0	B+
47	Westmont	190.0 µg/L	No	6	B-
48	North Aurora	190.0 µg/L	No	27	A-
49	Decatur	178.8 µg/L	No	28	B
50	Edwardsville	175.3 µg/L	No	18	D+
51	East St Louis	170.0 µg/L	No	1	B+
52	Northbrook	150.0 µg/L	No	55	D
53	Justice	149.4 µg/L	No	0	A-
54	Normal	147.4 µg/L	No	3	D+
55	Grays Lake	144.7 µg/L	No	6	A
56	Round Lake	140.0 µg/L	No	3	A-
57	Mundelein	136.9 µg/L	No	22	F
58	Lake Forest	135.8 µg/L	No	58	B-
59	Quincy	124.0 µg/L	No	3	B-
60	Gurnee	120.0 µg/L	No	4	A
61	Bridgeview	119.2 µg/L	No	0	A-
62	Hazel Crest	112.7 µg/L	No	2	B
63	Round Lake Beach	111.3 µg/L	No	3	B+
64	Godfrey	110.0 µg/L	No	22	C+
65	Libertyville	110.0 µg/L	No	14	C
66	Glenview	110.0 µg/L	No	3	B+
67	Geneva	110.0 µg/L	No	67	B-
68	Wilmette	110.0 µg/L	No	0	A
69	River Forest	110.0 µg/L	No	1	B+
70	Pekin	100.0 µg/L	No	1	D+
71	Rock Island	94.0 µg/L	No	5	B-
72	Highland Park	89.0 µg/L	No	2	B+
73	La Grange Park	85.7 µg/L	No	2	A
74	East Peoria	85.2 µg/L	No	133	F
75	Rockford	79.9 µg/L	No	43	F
76	Collinsville	73.0 µg/L	No	12	C-
77	Orion	72.8 µg/L	No	2	B-
78	Caseyville	66.0 µg/L	No	3	B+
79	Hickory Hills	63.0 µg/L	No	1	A
80	Lombard	62.0 µg/L	No	1	A-
81	Carbondale	53.2 µg/L	No	26	D
82	Taylorville	48.0 µg/L	No	0	A-
83	Bolingbrook	46.0 µg/L	No	2	A
84	Niles	46.0 µg/L	No	3	B
85	Wheeling	45.3 µg/L	No	5	A+
86	Buffalo Grove	43.1 µg/L	No	1	A
87	Crestwood	42.8 µg/L	No	0	B
88	Arlington Heights	37.3 µg/L	No	1	B-
89	Palatine	37.0 µg/L	No	2	B
90	Effingham	36.0 µg/L	No	2	A-
91	Morton Grove	34.0 µg/L	No	2	B-
92	Alsip	33.0 µg/L	No	2	A-
93	Rolling Meadows	32.0 µg/L	No	3	A
94	Naperville	30.0 µg/L	No	0	B+
95	Lisle	28.0 µg/L	No	2	A-
96	Elgin	26.0 µg/L	No	9	C-
97	Urbana	25.2 µg/L	No	0	C+
98	Woodridge	25.0 µg/L	No	2	A-
99	Palos Heights	25.0 µg/L	No	1	A-
100	Elk Grove	24.0 µg/L	No	2	A-
101	Brookfield	22.0 µg/L	No	0	A-
102	Ottawa	21.3 µg/L	No	62	F
103	Mount Prospect	21.0 µg/L	No	1	B+
104	Coleta	21.0 µg/L	No	1	A-
105	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. 43 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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