Water hardness in Seoul
73 mg/L moderately hard
Tap water in Seoul is moderately hard: 73 mg/L (4.2 gpg · 4.1 °dH · 7.3 °fH).
Source: K-water / 서울특별시 via data.go.kr (2025) · data checked 2026-10-20
Range across supply zones: 69–74 mg/L.
The municipal treatment plants serving Seoul had a 2025 median hardness of 72.5 mg/L CaCO₃, with plants ranging from 69.0 to 73.5 mg/L. Seoul's tap water is treated Han River water from the city's six purification centers. 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 | 73 mg/L |
|---|---|
| Utility | Seoul (서울특별시) |
How Seoul compares
- Tap water in Seoul is 28 % harder than the median of the 127 cities we track in South Korea (57 mg/L).
- By hardness it ranks 37 of 127 in South Korea (1 = hardest); 71 % of these cities have softer water.
- Nearest city with clearly softer water: Uijeongbu, 20 km away (30 mg/L).
- Nearest city with clearly harder water: Icheon, 52 km away (108 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 Seoul
| Brand | Setting for this water |
|---|---|
| Bosch | H00 |
| Miele | 4 °dH |
| AEG / Electrolux | 2 |
| Beko | 1st |
| Hoover | S1 |
| LG | H1 |
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 Seoul water hard or soft?
It is moderately hard: 73 mg/L as CaCO₃ (4.2 gpg, 4.1 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Seoul 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 Seoul water?
4.2 gpg, equal to 4.1 °dH, 7.3 °fH or 73 mg/L calcium carbonate.
What dishwasher salt setting should I use in Seoul?
For 73 mg/L (4.1 °dH) check your manufacturer's table: level 2–3.
Do I need a water softener in Seoul?
Not essential; a scale inhibitor protects the heater cheaply.
Source
Source: K-water / 서울특별시 via data.go.kr (2025). Method: figure published by the water supplier. K-water / 서울특별시 via data.go.kr · Outdated figure? Tell us