Illinois water hardness, by utility.

327 Illinois utilities serving 8.2 million people as they report it, from the state’s own results. Hardness is the calcium and magnesium in water; EPA sets no limit for it.

The short answer

Hard water reaches the most people here: 55 utilities serving 3.7 million. Another 71 utilities, serving 1.7 million, have water in more than one band.

The largest, Chicago, is hard, typically 137 mg/L (8 grains per gallon).

Very hard

Above 180 mg/L (10.5 grains per gallon). 113 utilities serving 1.5 million people; the 25 largest are here.

Illinois utilities: very hard water
Utility	Based in	Serves	Hardness, mg/L	Grains per gallon
Joliet	Joliet	160,000	224	13.1
Rockford	Rockford	147,051	313	18.3
IL American - Peoria	Peoria	137,575	267	15.6
Rock Island	Rock Island	39,018	215	12.6
Oswego	Oswego	38,169	235	13.7
North Park PWD	Machesney Park	35,580	395	23.1
IL American - Pekin	Pekin	31,731	289	16.9
Galesburg	Galesburg	31,620	280	16.4
Algonquin	Algonquin	30,700	385	22.5
Collinsville	Collinsville	30,616	230	13.4
Batavia	Batavia	26,098	304	17.8
Belvidere	Belvidere	25,339	380	22.2
Frankfort	Frankfort	24,000	561	32.8
Freeport	Freeport	23,930	415	24.3
Loves Park	Loves Park	23,335	270	15.8
Lockport	Lockport	23,100	541	31.6
East Peoria	East Peoria	22,484	415	24.3
McHenry	McHenry	22,335	470	27.5
Sycamore	Sycamore	18,500	289	16.9
North Aurora	North Aurora	18,261	235	13.7
Troy	Troy	16,962	560	32.8
Canton	Canton	16,748	328	19.2
Dixon	Dixon	15,096	305	17.8
Antioch	Antioch	14,175	270	15.8
Channahon	Channahon	13,380	273	16

All 113 with very hard water

Hard

121 to 180 mg/L (7.1 to 10.5 grains per gallon). 55 utilities serving 3.7 million people; the 25 largest are here.

Illinois utilities: hard water
Utility	Based in	Serves	Hardness, mg/L	Grains per gallon
Chicago	Chicago	2,721,308	137	8
Waukegan	Waukegan	87,149	140	8.2
Bloomington	Bloomington	79,000	135	7.9
Decatur	Decatur	76,122	130	7.6
Schaumburg	Schaumburg	75,750	132	7.7
Evanston	Evanston	74,486	130	7.6
Oak Lawn	Oak Lawn	58,362	140	8.2
Hanover Park	Hanover Park	37,470	135	7.9
Vernon Hills - Lake Co Pw	Vernon Hills	33,207	130	7.6
Gurnee	Gurnee	30,193	152	8.9
Highland Park	Highland Park	30,176	140	8.2
Aqua Illinois - Vermilion County	Danville	30,106	130	7.6
Aqua Illinois - North Maine Utilities	Glenview	30,043	130	7.6
Wilmette	Wilmette	27,650	135	7.9
Great Lakes Naval Training Station	North Chicago	23,000	130	7.6
South Holland	South Holland	22,000	140	8.2
Lake Forest	Lake Forest	19,642	140	8.2
IL American - Streator	Streator	19,000	173	10.1
Round Lake	Round Lake	18,430	140	8.2
North Chicago	North Chicago	16,813	130	7.6
Wildwood Subdivision - Lake Co Pw	Libertyville	14,073	130	7.6
Western Springs	Western Springs	13,629	131	7.7
Lincolnwood	Lincolnwood	13,463	136	8
Glen Carbon	Glen Carbon	12,618	122	7.1
Winnetka	Winnetka	12,475	140	8.2

All 55 with hard water

Moderately hard

61 to 120 mg/L (3.6 to 7 grains per gallon). 73 utilities serving 1.2 million people; the 25 largest are here.

Illinois utilities: moderately hard water
Utility	Based in	Serves	Hardness, mg/L	Grains per gallon
Springfield	Springfield	117,444	90	5.3
IL American - West Suburban	Bolingbrook	73,978	87	5.1
Glenview	Glenview	47,856	83	4.9
O Fallon	O Fallon	46,603	120	7
Moline	Moline	44,500	110	6.4
Quincy	Quincy	42,000	120	7
South Stickny SD	Burbank (South Stickney)	30,000	78	4.6
Ej Water Cooperative	Dieterich	29,720	113	6.6
Montgomery	Montgomery	28,956	76	4.4
Edwardsville	Edwardsville	26,808	110	6.4
Morton Grove	Morton Grove	25,297	85	5
West Chicago	West Chicago	25,166	99	5.8
IL American - Homer Township	Godfrey	24,543	81	4.7
Zion	Zion	24,442	87	5.1
Lisle	Lisle	24,223	79	4.6
Westmont	Westmont	24,161	120	7
Rolling Meadows	Rolling Meadows	23,329	89	5.2
Yorkville	Yorkville	23,000	81	4.8
Bloomingdale	Weston	22,018	76	4.4
Blue Island	Blue Island	21,494	83	4.8
Grayslake	Grays Lake	21,248	82	4.8
Geneva	Geneva	21,247	64	3.7
Libertyville	Libertyville	20,500	79	4.6
Evergreen Park	Evergreen Park	19,943	78	4.6
Mattoon	Mattoon	19,500	99	5.8

All 73 with moderately hard water

Soft

Up to 60 mg/L (3.5 grains per gallon). 15 utilities serving 116,694 people, largest first.

Illinois utilities: soft water
Utility	Based in	Serves	Hardness, mg/L	Grains per gallon
Carbondale	Carbondale	22,107	33	1.9
Mount Vernon	Mount Vernon	15,793	56	3.3
Lake of Egypt PWD	Marion	11,368	47	2.7
West Frankfort	West Frankfort	8,650	50	2.9
Gilberts	Gilberts	8,366	26	1.5
Greenville	Greenville	8,310	47	2.8
Benton	Benton	8,104	60	3.5
West Dundee	West Dundee	7,845	18	1.1
Clinton	Clinton	7,200	44	2.6
Eureka	Eureka	5,216	49	2.8
Tuscola	Tuscola	4,875	39	2.3
Wasco SD	Wasco	4,000	17	1
Metamora	Metamora	3,895	53	3.1
Altona	Altona	483	44	2.6
Buda	Buda	482	13	0.8

Varies

Water in more than one band, depending on where or when it was sampled: each is given as its range, softest to hardest, and its report says more. 71 utilities serving 1.7 million people; the 25 largest are here.

Illinois utilities: varies water
Utility	Based in	Serves	Hardness, mg/L	Grains per gallon
Aurora	Aurora	183,000	42 to 122	2.5 to 7.2
IL American - Champaign	Champaign	150,000	40 to 85	2.3 to 5
IL American - East St Louis	East St Louis	131,368	124 to 205	7.3 to 12
Elgin	Elgin	114,797	83 to 128	4.8 to 7.5
Aqua Illinois - Kankakee	Kankakee	80,000	132 to 440	7.7 to 25.7
Normal	Normal	52,736	89 to 560	5.2 to 32.7
Romeoville	Romeoville	50,458	89 to 597	5.2 to 34.9
IL American - Alton	Alton	46,127	132 to 221	7.7 to 12.9
Bartlett	Bartlett	41,500	133 to 638	7.8 to 37.3
Crystal Lake	Crystal Lake	40,661	1.6 to 91	0.1 to 5.3
Dekalb	De Kalb	40,290	110 to 190	6.4 to 11.1
Carpentersville	Carpentersville	37,983	150 to 290	8.8 to 17
Northbrook	Northbrook	34,200	79 to 140	4.6 to 8.2
IL American - Granite City	Granite City	33,572	113 to 224	6.6 to 13.1
St Charles	Saint Charles	33,081	100 to 560	5.8 to 32.7
Lake in the Hills	Lake in the Hills	28,661	12 to 560	0.7 to 32.7
Huntley	Huntley	28,495	19 to 62	1.1 to 3.6
Woodstock	Woodstock	25,630	100 to 250	5.8 to 14.6
South Elgin	South Elgin	23,648	7.7 to 510	0.5 to 29.8
Park Forest	Park Forest	21,687	145 to 200	8.5 to 11.7
East Moline	East Moline	21,374	180 to 220	10.5 to 12.9
Crest Hill	Crest Hill	20,223	7.1 to 618	0.4 to 36.1
Jacksonville	Jacksonville	19,903	120 to 130	7 to 7.6
Lake Zurich	Lake Zurich	19,759	57 to 100	3.4 to 5.8
Shorewood	Shorewood	18,645	71 to 390	4.1 to 22.8

All 71 whose water varies

Source: Illinois Environmental Protection Agency, Bureau of Water, 327 utilities, results from Aug. 2, 2016 to July 29, 2026, read Oct. 17, 2026. Each sampling point is taken at its median; a figure is typical where every point falls in one band.

Bands are the U.S. Geological Survey’s, at 17.1 mg/L to the grain. People served is what each utility reports; where one sells water to another, the same people can be counted twice. How hardness is measured here.

Very hard

Hard

Moderately hard

Soft

Varies

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