Water hardness in St. Louis
7.5 gpg hard
Tap water in St. Louis is hard: 7.5 gpg (129 mg/L · 7.2 °dH · 12.9 °fH).
Source: City of St. Louis 2025 Consumer Confidence Report (2025) · data checked 2026-10-19
Range across supply zones: 80–206 mg/L.
The City of St. Louis 2025 consumer confidence report gives total hardness as CaCO3 of 129 mg/L (7.5 gpg), with a range of 80 to 206 mg/L. It also lists non-carbonate hardness separately, which this page does not use. The water is hard, with visible scale likely on kettles and shower screens.
USGS classes: soft 0–60, moderately hard 61–120, hard 121–180, very hard >180 mg/L.
Water data
| Total hardness | 7.5 gpg |
|---|---|
| Utility | City of St. Louis Water Division |
How St. Louis compares
- Tap water in St. Louis is 17 % softer than the median of the 1372 cities we track in the United States (9.1 gpg).
- By hardness it ranks 840 of 1372 in the United States (1 = hardest); 39 % of these cities have softer water.
- In Missouri it is number 26 of 32 cities; the regional median is 10.3 gpg.
- Nearest city with clearly softer water: Ironton, 121 km away (6 gpg).
- Nearest city with clearly harder water: Maplewood, 11 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. Louis
| Brand | Setting for this water |
|---|---|
| Bosch | H01 |
| Miele | 7 °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 St. Louis water hard or soft?
It is hard: 129 mg/L as CaCO₃ (7.5 gpg, 7.2 °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. Louis 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. Louis water?
7.5 gpg, equal to 7.2 °dH, 12.9 °fH or 129 mg/L calcium carbonate.
What dishwasher salt setting should I use in St. Louis?
For 129 mg/L (7.2 °dH) check your manufacturer's table: level 4–5.
Do I need a water softener in St. Louis?
Recommended if you have a water heater, boiler or tankless unit: it saves repairs and detergent.
Source
Source: City of St. Louis 2025 Consumer Confidence Report (2025). Method: figure published by the water supplier. City of St. Louis 2025 Consumer Confidence Report · Outdated figure? Tell us