WaterProfile Local

Utilities / Illinois

Chicago, IL water hardness

City of Chicago Department of Water Management does not publish one hardness figure for Chicago. It publishes 2 separate figures, one per treatment plant, in its Comprehensive Chemical Analysis, 2025 (Bureau of Water Supply, Water Quality Division). Across them the published numbers run from 126 to 143 mg/L. On the USGS scale those figures are all hard water, so the classification does not depend on which treatment plant serves an address. Every published figure is in the table below.

Soft Moderate Hard Very hard 0 60 120 180 500+ 134.5 mg/L Chicago, IL spans 2 published treatment plants, all in the hard band mg/L as CaCO₃. Bands drawn equal width, so the axis is not linear.
City of Chicago Department of Water Management published a figure for each of 2 treatment plants rather than one for the system; the bar spans the lowest and highest of those published figures, 126 to 143 mg/L. The plotted point is the midpoint of the lowest and highest figures published across this system's 2 areas; the utility publishes no system-wide figure, so this midpoint is not one of its numbers. Classification bands from the USGS Water Science School.

Every figure City of Chicago Department of Water Management publishes, by treatment plant

These are the only hardness numbers this utility publishes. There is no system-wide figure to quote, so the figure plotted above is a midpoint we calculated from the lowest and highest of them, and it is labelled as such everywhere it appears.

Treatment plant as publishedmg/L (ppm)Grains per gallonUSGS class
South Water Purification Plant (outlets and South distribution) 12 results: two plant outlets and one distribution point, each sampled once a quarter. 128–143 7.5–8.4 Hard
Jardine Water Purification Plant (outlets and Central/North distribution) 16 results: two plant outlets and two distribution points, each sampled once a quarter. 126–143 7.4–8.4 Hard

Figures in the grains column are the utility's own where it published them. Where it published only one unit, the other column is our conversion at 17.1 mg/L per grain, and the row above says which. Nothing in this table is averaged across treatment plants.

The published figures, exactly as they appear

This is the hardness line transcribed from the source, with nothing added:

HARDNESS, as CaCO3, mg/L, SM 2340 C. South Water Purification Plant (2A Outlet 73rd Street, 2B Outlet 79th Street, 3 Distribution South): 1st Quarter 142 142 143; 2nd Quarter 143 143 143; 3rd Quarter 134 134 142; 4th Quarter 128 131 135. Jardine Water Purification Plant (5A Outlet North, 5B Outlet Central, 6 Distribution Central, 7 Distribution North): 1st Quarter 141 142 143 143; 2nd Quarter 142 142 143 143; 3rd Quarter 134 136 141 141; 4th Quarter 126 129 140 138

City of Chicago Department of Water Management, Comprehensive Chemical Analysis, 2025 (Bureau of Water Supply, Water Quality Division)

Units as published: as CaCO3, mg/L. What kind of figure it is: figures for each treatment plant, with no system-wide figure. Retrieved 2026-10-26.

Chicago hardness in mg/L and grains per gallon

Water-quality reports use mg/L (identical to ppm). Softener instructions and plumbing specifications use grains per gallon. Both are below. Where a figure is our arithmetic rather than the utility's own number, it says so.

Figuremg/L (ppm)Grains per gallonWhose number
Low end of published span across areas1267.4mg/L published, gpg is our conversion
High end of published span across areas1438.4mg/L published, gpg is our conversion
Plotted on the scale above134.57.9midpoint of the lowest and highest figures published across this system's 2 areas; the utility publishes no system-wide figure, so this midpoint is not one of its numbers; the gpg here is our conversion at 17.1, so it can differ slightly from a utility’s own rounded gpg figure

The conversion, both ways: gpg = mg/L ÷ 17.1 and mg/L = gpg × 17.1. Worked for this system: 134.5 ÷ 17.1 = 7.9 gpg. The converter does °dH and °f as well, and why the factor is 17.1 explains where the number comes from.

What this figure does not tell you

Service area and source water

UtilityCity of Chicago Department of Water Management
Service area as publishedThe City of Chicago, supplied by two purification plants on Lake Michigan. The analysis does not say which addresses each plant serves.
Source waterLake Michigan.

Provenance of every number on this page

Source documentComprehensive Chemical Analysis, 2025 (Bureau of Water Supply, Water Quality Division)
Source URLhttps://www.chicago.gov/content/dam/city/depts/water/WaterQltyResultsNRpts/ccReports/CompChem_2025.pdf
Published byCity of Chicago Department of Water Management
Report year2025
Year noteFour quarterly sampling rounds: January 6-8, April 7-9, July 7-9 and October 6-8, 2025. The document is a scanned image; the figures were read from the page images.
Retrieved2026-10-26
Classification bandsUSGS Water Science School, retrieved 2026-10-16

Notes the report forces on this page

If you are sizing a softener for Chicago water

At 7.9 gpg, the sizing arithmetic starts from your household's water use, not from the hardness alone. The calculator below is pre-filled with this system's figure and every other input is an editable assumption.

Whether a softener is worth installing at this hardness is a judgement, not arithmetic, and it is not one this site makes for you. Nothing here has been tested by the author.

Where Chicago sits against other verified systems

Soft Soft 0–60
Moderately hard Moderate 61–120
Hard Hard 121–180
Very hard Very hard 181+
  1. Portland, OR 9 mg/L 0.5 gpg Soft
  2. Boston, MA 16 mg/L 1 gpg Soft
  3. Manchester, NH 17.9 mg/L 1 gpg Soft
  4. Seattle, WA 19.1 mg/L 1.1 gpg Soft
  5. Raleigh, NC 25 mg/L 1.47 gpg Soft
  6. New York, NY 32 mg/L 2 gpg Soft
  7. Charlotte, NC 32 mg/L 1.9 gpg Soft
  8. Memphis, TN 46 mg/L 2.7 gpg Soft
  9. Norfolk, VA 48 mg/L 2.8 gpg Soft
  10. Anchorage, AK 56 mg/L 3.3 gpg Soft
  11. Virginia Beach, VA 56 mg/L 3.3 gpg Soft
  12. Oakland, CA 68.4 mg/L 4 gpg Moderately hard
  13. Nashville, TN 77.3 mg/L 4.5 gpg Moderately hard
  14. Sacramento, CA 83 mg/L 4.9 gpg Moderately hard
  15. Fresno, CA 89.3 mg/L 5.2 gpg Moderately hard
  16. Saint Paul, MN 90 mg/L 5 gpg Moderately hard
  17. Austin, TX 93 mg/L 5.4 gpg Moderately hard
  18. Minneapolis, MN 94 mg/L 5.5 gpg Moderately hard
  19. Washington, DC 95 mg/L 5.6 gpg Moderately hard
  20. Baltimore, MD 97.5 mg/L 5.7 gpg Moderately hard
  21. Birmingham, AL 98 mg/L 5.7 gpg Moderately hard
  22. Kansas City, MO 100 mg/L 5.8 gpg Moderately hard
  23. Denver, CO 105 mg/L 6.1 gpg Moderately hard
  24. Detroit, MI 107 mg/L 6.3 gpg Moderately hard
  25. Aurora, CO 113 mg/L 6.6 gpg Moderately hard
  26. Tulsa, OK 114.5 mg/L 6.7 gpg Moderately hard
  27. Louisville, KY 115 mg/L 6.7 gpg Moderately hard
  28. Columbus, OH 120 mg/L 7 gpg Moderately hard
  29. Cleveland, OH 120 mg/L 7 gpg Moderately hard
  30. Philadelphia, PA 125 mg/L 7.3 gpg Hard
  31. Ann Arbor, MI 126 mg/L 7.4 gpg Hard
  32. Cincinnati, OH 133 mg/L 7.8 gpg Hard
  33. Chicago, IL 134.5 mg/L 7.9 gpg Hard
  34. Houston, TX 135.5 mg/L 7.9 gpg Hard
  35. Milwaukee, WI 137 mg/L 8.01 gpg Hard
  36. St. Louis, MO 138 mg/L 8.1 gpg Hard
  37. Grand Rapids, MI 142 mg/L 8.3 gpg Hard
  38. Fort Worth, TX 145 mg/L 8.5 gpg Hard
  39. Spokane, WA 159 mg/L 9.3 gpg Hard
  40. Honolulu, HI 162.5 mg/L 9.5 gpg Hard
  41. Wichita, KS 170 mg/L 9.9 gpg Hard
  42. Omaha, NE 170 mg/L 10 gpg Hard
  43. Los Angeles, CA 192 mg/L 11.2 gpg Very hard
  44. Lincoln, NE 192 mg/L 11.2 gpg Very hard
  45. Riverside, CA 197 mg/L 12 gpg Very hard
  46. Tampa, FL 220 mg/L 12.9 gpg Very hard
  47. Phoenix, AZ 237 mg/L 13.9 gpg Very hard
  48. Mesa, AZ 239.4 mg/L 14 gpg Very hard
  49. Round Rock, TX 258 mg/L 15.1 gpg Very hard
  50. Pflugerville, TX 267 mg/L 15.6 gpg Very hard
  51. San Diego, CA 276 mg/L 16 gpg Very hard
  52. Las Vegas, NV 280 mg/L 16 gpg Very hard
  53. Chandler, AZ 282.2 mg/L 16.5 gpg Very hard
  54. San Antonio, TX 299.3 mg/L 17.5 gpg Very hard
  55. Anaheim, CA 300 mg/L 18 gpg Very hard
  56. Henderson, NV 304 mg/L 18 gpg Very hard
  57. Indianapolis, IN 317 mg/L 19 gpg Very hard
  58. Madison, WI 324.9 mg/L 19 gpg Very hard
  59. Scottsdale, AZ 352.5 mg/L 20.6 gpg Very hard
  60. Salt Lake City, UT 353.5 mg/L 20.7 gpg Very hard

mg/L as calcium carbonate. Each classification band is drawn the same width, so the axis is not linear in mg/L.

Chicago, IL is the highlighted row. Every other system on this chart has its own page with its own published figure and report date. Grains per gallon are the utility's own figure where it published one, and our conversion at 17.1 mg/L per grain where it did not.

Systems with similar published hardness

All 60 verified systems   How to find hardness in your own utility's report   If you are on a well instead