Water hardness in Gongju
66 mg/L moderately hard
Tap water in Gongju is moderately hard: 66 mg/L (3.9 gpg · 3.7 °dH · 6.6 °fH).
Source: K-water / 충청남도 공주시 via data.go.kr (2025) · data checked 2026-10-20
Range across supply zones: 52–80 mg/L.
The municipal treatment plants serving Gongju had a 2025 median hardness of 66.0 mg/L CaCO₃, with plants ranging from 52.0 to 80.0 mg/L. This area belongs to the Geum River basin, where Daecheong Dam supplies water; the utility's own raw-water source is not confirmed here. At this level a white film forms on kettles and shower screens, and water heaters collect scale slowly over the years.
Korean waterworks report hardness (경도) in mg/L CaCO₃; the drinking-water standard is 300 mg/L (1,000 mg/L for some sources).
Water data
| Total hardness | 66 mg/L |
|---|---|
| Utility | Gongju-si (충청남도 공주시) |
How Gongju compares
- Tap water in Gongju is 16 % harder than the median of the 127 cities we track in South Korea (57 mg/L).
- By hardness it ranks 50 of 127 in South Korea (1 = hardest); 60 % of these cities have softer water.
- In Chungcheongnam-do it is number 4 of 5 cities; the regional median is 75 mg/L.
- Nearest city with clearly softer water: Daejeon, 26 km away (53 mg/L).
- Nearest city with clearly harder water: Cheonan, 39 km away (124 mg/L).
Ranking of the hardest and softest water in South Korea →
What it means at home
- Visible kettle scale every few weeks; vinegar or citric acid is enough.
- Water heater and washing machine: some long-term scale; a scale inhibitor slows it.
- Dishwasher: medium salt setting.
- Softener optional; pays off mainly with a gas boiler or tankless heater.
How much salt will you use for softening?
Optional. A scale inhibitor or a small softener protects the heater; soap savings are modest.
Descale a coffee machine or kettle about every 3 months (typical manufacturer guidance for this hardness).
Estimates for planning, not a quote. Check your appliance manual for exact settings.
Dishwasher setting in Gongju
| Brand | Setting for this water |
|---|---|
| Bosch | H00 |
| Miele | 4 °dH |
| AEG / Electrolux | 1 |
| Beko | 1st |
| Hoover | S0 |
| LG | H0 |
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 Gongju water hard or soft?
It is moderately hard: 66 mg/L as CaCO₃ (3.9 gpg, 3.7 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Gongju safe to drink?
Hardness is not a health issue; it is about limescale, taste and appliances. Mains water must meet national drinking-water standards. Korean waterworks report hardness (경도) in mg/L CaCO₃; the drinking-water standard is 300 mg/L (1,000 mg/L for some sources).
How many grains per gallon is Gongju water?
3.9 gpg, equal to 3.7 °dH, 6.6 °fH or 66 mg/L calcium carbonate.
What dishwasher salt setting should I use in Gongju?
For 66 mg/L (3.7 °dH) check your manufacturer's table: level 2–3.
Do I need a water softener in Gongju?
Not essential; a scale inhibitor protects the heater cheaply.
Source
Source: K-water / 충청남도 공주시 via data.go.kr (2025). Method: figure published by the water supplier. K-water / 충청남도 공주시 via data.go.kr · Outdated figure? Tell us