Water hardness in Hakone
110 mg/L moderately hard
Tap water in Hakone is moderately hard: 110 mg/L (6.4 gpg · 6.2 °dH · 11 °fH).
Source: Kanagawa Prefectural Waterworks, annual water quality report FY2024 (令和6年度 県営水道の水質), 箱根水道センター taps (2024) · data checked 2026-10-21
Range across supply zones: 65–160 mg/L.
Hakone is served by Kanagawa Prefectural Waterworks from spring sources such as those at Sengokuhara, in volcanic terrain unlike the lowland river supplies elsewhere in the prefecture. The utility's 2024 data give 110.0 mg/L CaCO₃ within a range of 65.0 to 160.0 mg/L. This is hard water for Japan: expect fast scale in kettles and heaters, and consider a softener to protect them.
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 | 110 mg/L |
|---|---|
| Utility | Kanagawa Prefectural Waterworks (神奈川県企業庁 県営水道, 箱根水道センター) |
How Hakone compares
- Tap water in Hakone is 119 % harder than the median of the 228 cities we track in Japan (50 mg/L).
- By hardness it ranks 2 of 228 in Japan (1 = hardest); 100 % of these cities have softer water.
- In Kanagawa it is number 1 of 12 cities; the regional median is 62 mg/L.
- Nearest city with clearly softer water: Odawara, 14 km away (60 mg/L).
Ranking of the hardest and softest water in Japan →
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 Hakone
| Brand | Setting for this water |
|---|---|
| Bosch | H00 |
| Miele | 6 °dH |
| AEG / Electrolux | 2 |
| Beko | 2nd |
| 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 Hakone water hard or soft?
It is moderately hard: 110 mg/L as CaCO₃ (6.4 gpg, 6.2 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Hakone 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 Hakone water?
6.4 gpg, equal to 6.2 °dH, 11 °fH or 110 mg/L calcium carbonate.
What dishwasher salt setting should I use in Hakone?
For 110 mg/L (6.2 °dH) check your manufacturer's table: level 2–3.
Do I need a water softener in Hakone?
Not essential; a scale inhibitor protects the heater cheaply.
Source
Source: Kanagawa Prefectural Waterworks, annual water quality report FY2024 (令和6年度 県営水道の水質), 箱根水道センター taps (2024). Method: figure published by the water supplier. Kanagawa Prefectural Waterworks, annual water quality report FY2024 (令和6年度 県営水道の水質), 箱根水道センター taps · Outdated figure? Tell us