Water hardness in Jeju
31 mg/L soft
Tap water in Jeju is soft: 31 mg/L (1.8 gpg · 1.7 °dH · 3 °fH).
Source: K-water / 제주특별자치도 via data.go.kr (2025) · data checked 2026-10-20
Range across supply zones: 2–52 mg/L.
The municipal treatment plants serving Jeju had a 2025 median hardness of 30.5 mg/L CaCO₃, with plants ranging from 2.0 to 52.0 mg/L. Jeju has no perennial rivers; its drinking water comes almost entirely from groundwater in young, highly permeable basalt aquifers, which keeps mineral content low. Soft water leaves little limescale on taps and appliances; detergent doses can usually stay at the low end of the label. The spread between plants is wide, so check which plant serves your street.
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 | 31 mg/L |
|---|---|
| Utility | Jeju-do (제주특별자치도) |
How Jeju compares
- Tap water in Jeju is 46 % softer than the median of the 127 cities we track in South Korea (57 mg/L).
- By hardness it ranks 108 of 127 in South Korea (1 = hardest); 15 % of these cities have softer water.
- Nearest city with clearly softer water: Wando, 91 km away (16 mg/L).
- Nearest city with clearly harder water: Haenam, 118 km away (40 mg/L).
Ranking of the hardest and softest water in South Korea →
What it means at home
- Little or no limescale in kettles, water heaters or washing machines.
- Soap lathers easily; water does not dry skin or hair.
- Dishwasher: salt setting at minimum or off.
- No softener needed; a jug filter only changes taste.
How much salt will you use for softening?
No. Water this soft does not need softening.
Descale a coffee machine or kettle about every 6 months (typical manufacturer guidance for this hardness).
Estimates for planning, not a quote. Check your appliance manual for exact settings.
Dishwasher setting in Jeju
| Brand | Setting for this water |
|---|---|
| Bosch | H00 |
| Miele | 2 °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 Jeju water hard or soft?
It is soft: 31 mg/L as CaCO₃ (1.8 gpg, 1.7 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Jeju 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 Jeju water?
1.8 gpg, equal to 1.7 °dH, 3 °fH or 31 mg/L calcium carbonate.
What dishwasher salt setting should I use in Jeju?
For 31 mg/L (1.7 °dH) check your manufacturer's table: level 0–1, usually no salt.
Do I need a water softener in Jeju?
No. With soft water a softener adds nothing.
Source
Source: K-water / 제주특별자치도 via data.go.kr (2025). Method: figure published by the water supplier. K-water / 제주특별자치도 via data.go.kr · Outdated figure? Tell us