Water hardness in Sun Prairie
18.7 gpg very hard
Tap water in Sun Prairie is very hard: 18.7 gpg (320 mg/L · 17.9 °dH · 32 °fH).
Source: Wisconsin DNR Drinking Water System portal (Sun Prairie Utilities) (2026) · data checked 2026-10-20
Range across supply zones: 270–370 mg/L.
Sun Prairie pumps groundwater from Dane County wells, mostly in the deep sandstone aquifer. Dane County groundwater is among Wisconsin's hardest, and the city's wells give 320 mg/L CaCO₃ (270–370 mg/L). Heavy scale on heaters and glass.
USGS classes: soft 0–60, moderately hard 61–120, hard 121–180, very hard >180 mg/L.
Water data
| Total hardness | 18.7 gpg |
|---|---|
| Utility | Sun Prairie Utilities |
How Sun Prairie compares
- Tap water in Sun Prairie is 106 % harder than the median of the 1372 cities we track in the United States (9.1 gpg).
- By hardness it ranks 189 of 1372 in the United States (1 = hardest); 86 % of these cities have softer water.
- In Wisconsin it is number 110 of 448 cities; the regional median is 14.3 gpg.
- Nearest city with clearly softer water: Dane, 22 km away (14.6 gpg).
- Nearest city with clearly harder water: Monona, 16 km away (26.9 gpg).
Ranking of the hardest and softest water in the United States →
What it means at home
- Severe scale: heater elements and washing-machine heaters fail early.
- Detergent use is very high; taps and screens coat within days.
- Dishwasher at maximum salt setting.
- An ion-exchange softener is practically essential; RO for drinking water.
How much salt will you use for softening?
Yes. At this hardness a softener pays for itself through appliance life and detergent.
Descale a coffee machine or kettle about every 1 months (typical manufacturer guidance for this hardness).
Estimates for planning, not a quote. Check your appliance manual for exact settings.
Dishwasher setting in Sun Prairie
| Brand | Setting for this water |
|---|---|
| Bosch | H05 |
| Miele | 18 °dH |
| AEG / Electrolux | 4 |
| Beko | 5th |
| Hoover | S3 |
| LG | H3 |
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 Sun Prairie water hard or soft?
It is very hard: 320 mg/L as CaCO₃ (18.7 gpg, 17.9 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Sun Prairie 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 Sun Prairie water?
18.7 gpg, equal to 17.9 °dH, 32 °fH or 320 mg/L calcium carbonate.
What dishwasher salt setting should I use in Sun Prairie?
For 320 mg/L (17.9 °dH) check your manufacturer's table: maximum level (5–7).
Do I need a water softener in Sun Prairie?
Yes, unless you are only passing through: scale damages appliances within a few years.
Source
Source: Wisconsin DNR Drinking Water System portal (Sun Prairie Utilities) (2026). Method: figure published by the water supplier. Wisconsin DNR Drinking Water System portal (Sun Prairie Utilities) · Outdated figure? Tell us