Water hardness in Hachioji
56 mg/L soft
Tap water in Hachioji is soft: 56 mg/L (3.3 gpg · 3.1 °dH · 5.6 °fH).
Source: Tokyo Metropolitan Waterworks Bureau (東京都水道局), tap-water quality results FY2025 (2025) · data checked 2026-10-21
Range across supply zones: 48–66 mg/L.
Hachioji is supplied by the Tokyo Metropolitan Waterworks Bureau, which draws about 80% of its water resources from the Tone and Arakawa river systems and about 20% from the Tama River system, with groundwater adding to the supply in the Tama area. Hardness is reported at 56.2 mg/L CaCO₃, ranging from 48.1 to 66.1 mg/L (2025 data). Moderately soft water leaves visible deposits on kettles and taps over time, which regular descaling keeps in check.
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 | 56 mg/L |
|---|---|
| Utility | Tokyo Metropolitan Waterworks Bureau (東京都水道局) |
How Hachioji compares
- Tap water in Hachioji is 12 % harder than the median of the 228 cities we track in Japan (50 mg/L).
- By hardness it ranks 94 of 228 in Japan (1 = hardest); 59 % of these cities have softer water.
- In Tokyo it is number 41 of 53 cities; the regional median is 62 mg/L.
- Nearest city with clearly softer water: Akiruno, 12 km away (42 mg/L).
- Nearest city with clearly harder water: Mitaka, 22 km away (71 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 Hachioji
| Brand | Setting for this water |
|---|---|
| Bosch | H00 |
| Miele | 3 °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 Hachioji water hard or soft?
It is soft: 56 mg/L as CaCO₃ (3.3 gpg, 3.1 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Hachioji 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 Hachioji water?
3.3 gpg, equal to 3.1 °dH, 5.6 °fH or 56 mg/L calcium carbonate.
What dishwasher salt setting should I use in Hachioji?
For 56 mg/L (3.1 °dH) check your manufacturer's table: level 0–1, usually no salt.
Do I need a water softener in Hachioji?
No. With soft water a softener adds nothing.
Source
Source: Tokyo Metropolitan Waterworks Bureau (東京都水道局), tap-water quality results FY2025 (2025). Method: figure published by the water supplier. Tokyo Metropolitan Waterworks Bureau (東京都水道局), tap-water quality results FY2025 · Outdated figure? Tell us