Water hardness in Chicago
7.9 gpg hard
Tap water in Chicago is hard: 7.9 gpg (135 mg/L · 7.6 °dH · 13.5 °fH).
Source: City of Chicago DWM, Comprehensive Chemical Analysis 2025 (quarterly, plant outlets) (2025) · data checked 2026-10-22
Range across supply zones: 126–143 mg/L.
2 supply zones — hardness varies by neighbourhood; the figure above is the median.
Hardness by district / supply zone
| gpg | mg/L | ||
|---|---|---|---|
| Jardine Water Purification Plant service area | 7.9 | 136 | hard |
| South Water Purification Plant service area | 7.8 | 134 | hard |
Chicago takes all of its water from Lake Michigan through offshore intakes and treats it at the Jardine plant on the north side and the Sawyer plant on the south side. Lake water picks up carbonate from the limestone and dolomite around its basin, which gives a hardness of 135 mg/L CaCO₃. The two supply areas differ only slightly (126–143 mg/L), so scale in kettles and water heaters looks much the same across the city.
USGS classes: soft 0–60, moderately hard 61–120, hard 121–180, very hard >180 mg/L.
Water data
| Total hardness | 7.9 gpg |
|---|---|
| Utility | City of Chicago Department of Water Management |
How Chicago compares
- Tap water in Chicago is 13 % softer than the median of the 1372 cities we track in the United States (9.1 gpg).
- By hardness it ranks 800 of 1372 in the United States (1 = hardest); 41 % of these cities have softer water.
- In Illinois it is number 10 of 14 cities; the regional median is 8 gpg.
- Nearest city with clearly softer water: Bloomfield, 95 km away (1 gpg).
- Nearest city with clearly harder water: Bristol, 79 km away (14 gpg).
Ranking of the hardest and softest water in the United States →
What it means at home
- Fast scale on taps, shower screens and kettle; white spots on glassware.
- Water heater: efficiency loss and element failures within years if unprotected.
- Dry skin and dull hair after showering are common.
- Softener recommended; jug or reverse osmosis for drinking.
How much salt will you use for softening?
Recommended, especially with a heater or boiler: scale cuts efficiency and shortens its life.
Descale a coffee machine or kettle about every 2 months (typical manufacturer guidance for this hardness).
Estimates for planning, not a quote. Check your appliance manual for exact settings.
Dishwasher setting in Chicago
| Brand | Setting for this water |
|---|---|
| Bosch | H01 |
| Miele | 8 °dH |
| AEG / Electrolux | 2 |
| Beko | 2nd |
| Hoover | S1 |
| LG | H2 |
From each brand's manual for the model family named in the source; your model may differ, so check its manual. All brands and how to change the setting →
FAQ
Is Chicago water hard or soft?
It is hard: 135 mg/L as CaCO₃ (7.9 gpg, 7.6 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Chicago safe to drink?
Hardness is not a health issue; it is about limescale, taste and appliances. Mains water must meet national drinking-water standards. USGS classes: soft 0–60, moderately hard 61–120, hard 121–180, very hard >180 mg/L.
How many grains per gallon is Chicago water?
7.9 gpg, equal to 7.6 °dH, 13.5 °fH or 135 mg/L calcium carbonate.
What dishwasher salt setting should I use in Chicago?
For 135 mg/L (7.6 °dH) check your manufacturer's table: level 4–5.
Do I need a water softener in Chicago?
Recommended if you have a water heater, boiler or tankless unit: it saves repairs and detergent.
Source
Source: City of Chicago DWM, Comprehensive Chemical Analysis 2025 (quarterly, plant outlets) (2025). Method: own measurement. City of Chicago DWM, Comprehensive Chemical Analysis 2025 (quarterly, plant outlets) · Outdated figure? Tell us