Water hardness in Nagasaki
25 mg/L soft
Tap water in Nagasaki is soft: 25 mg/L (1.5 gpg · 1.4 °dH · 2.5 °fH).
Source: 長崎市上下水道局 Nagasaki City Waterworks and Sewerage Bureau, monthly tap-water quality results FY2025 (2025) · data checked 2026-10-21
Range across supply zones: 14–87 mg/L.
Nagasaki has few large rivers and relies on dams for more than 80% of its supply, among them Motogōchi, Urakami and Ogura. The utility's 2025 data give 25.0 mg/L CaCO₃ within a range of 13.8 to 87.4 mg/L; the spread is wide, so the value at your tap depends on where in the supply area you live. At this level scale is rarely a problem, soap lathers easily and a softener is unnecessary.
Japanese waterworks report hardness (硬度) in mg/L CaCO₃; the standard is 300 mg/L and the target 10–100 mg/L.
Water data
| Total hardness | 25 mg/L |
|---|---|
| Utility | Nagasaki City Waterworks and Sewerage Bureau |
How Nagasaki compares
- Tap water in Nagasaki is 50 % softer than the median of the 228 cities we track in Japan (50 mg/L).
- By hardness it ranks 211 of 228 in Japan (1 = hardest); 7 % of these cities have softer water.
- Nearest city with clearly harder water: Sasebo, 49 km away (46 mg/L).
Ranking of the hardest and softest water in Japan →
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 Nagasaki
| Brand | Setting for this water |
|---|---|
| Bosch | H00 |
| Miele | 1 °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 Nagasaki water hard or soft?
It is soft: 25 mg/L as CaCO₃ (1.5 gpg, 1.4 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Nagasaki safe to drink?
Hardness is not a health issue; it is about limescale, taste and appliances. Mains water must meet national drinking-water standards. Japanese waterworks report hardness (硬度) in mg/L CaCO₃; the standard is 300 mg/L and the target 10–100 mg/L.
How many grains per gallon is Nagasaki water?
1.5 gpg, equal to 1.4 °dH, 2.5 °fH or 25 mg/L calcium carbonate.
What dishwasher salt setting should I use in Nagasaki?
For 25 mg/L (1.4 °dH) check your manufacturer's table: level 0–1, usually no salt.
Do I need a water softener in Nagasaki?
No. With soft water a softener adds nothing.
Source
Source: 長崎市上下水道局 Nagasaki City Waterworks and Sewerage Bureau, monthly tap-water quality results FY2025 (2025). Method: figure published by the water supplier. 長崎市上下水道局 Nagasaki City Waterworks and Sewerage Bureau, monthly tap-water quality results FY2025 · Outdated figure? Tell us