Water hardness in St. Peters
10.1 gpg hard
Tap water in St. Peters is hard: 10.1 gpg (173 mg/L · 9.7 °dH · 17.3 °fH).
Source: St. Peters PWS 2025 Annual Water Quality Report (Missouri DNR copy), p3 (2025) · data checked 2026-10-20
The St. Peters public water system's 2025 report, filed with Missouri DNR, lists calcium at 27.8 mg/L and magnesium at 25.2 mg/L. We computed hardness from those two figures: 173 mg/L (about 10.1 gpg), which is hard. The report gives one value rather than a range, so tap water at your address may differ a little. Expect visible scale on kettles and heaters, and consider a softener.
USGS classes: soft 0–60, moderately hard 61–120, hard 121–180, very hard >180 mg/L.
Water data
| Total hardness | 10.1 gpg |
|---|---|
| Calcium (mg/L) | 27.8 |
| Magnesium (mg/L) | 25.2 |
| Utility | St. Peters PWS (PWSID MO6010719) |
How St. Peters compares
- Tap water in St. Peters is 12 % harder than the median of the 1372 cities we track in the United States (9.1 gpg).
- By hardness it ranks 620 of 1372 in the United States (1 = hardest); 55 % of these cities have softer water.
- In Missouri it is number 18 of 32 cities; the regional median is 10.3 gpg.
- Nearest city with clearly softer water: St. Louis, 41 km away (7.5 gpg).
- Nearest city with clearly harder water: Maplewood, 33 km away (14.4 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 St. Peters
| Brand | Setting for this water |
|---|---|
| Bosch | H02 |
| Miele | 10 °dH |
| AEG / Electrolux | 2 |
| Beko | 3rd |
| 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 St. Peters water hard or soft?
It is hard: 173 mg/L as CaCO₃ (10.1 gpg, 9.7 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in St. Peters 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 St. Peters water?
10.1 gpg, equal to 9.7 °dH, 17.3 °fH or 173 mg/L calcium carbonate.
What dishwasher salt setting should I use in St. Peters?
For 173 mg/L (9.7 °dH) check your manufacturer's table: level 4–5.
Do I need a water softener in St. Peters?
Recommended if you have a water heater, boiler or tankless unit: it saves repairs and detergent.
Source
Source: St. Peters PWS 2025 Annual Water Quality Report (Missouri DNR copy), p3 (2025). Method: computed from supplier's calcium and magnesium. St. Peters PWS 2025 Annual Water Quality Report (Missouri DNR copy), p3 · Outdated figure? Tell us