Water hardness in Hiroshima
20 mg/L soft
Tap water in Hiroshima is soft: 20 mg/L (1.2 gpg · 1.1 °dH · 2 °fH).
Source: 広島市水道局 Hiroshima City Waterworks Bureau, tap-water quality results by supply system FY2025 (2025) · data checked 2026-10-21
Range across supply zones: 11–43 mg/L.
Hiroshima draws on the Ōta River and the Haji Dam reservoir in the Gō River basin, and also receives water from the Hiroshima Prefecture waterworks union. The reported figure is 19.9 mg/L CaCO₃ (range 10.6 to 43.4 mg/L, 2025 data); the spread is wide, so the value at your tap depends on where in the supply area you live. Water this soft rarely leaves scale, so kettles and showerheads stay mostly clear and a softener adds little.
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 | 20 mg/L |
|---|---|
| Utility | Hiroshima City Waterworks Bureau |
How Hiroshima compares
- Tap water in Hiroshima is 60 % softer than the median of the 228 cities we track in Japan (50 mg/L).
- By hardness it ranks 219 of 228 in Japan (1 = hardest); 4 % of these cities have softer water.
- In Hiroshima it is number 3 of 3 cities; the regional median is 20 mg/L.
- Nearest city with clearly harder water: Matsuyama, 69 km away (68 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 Hiroshima
| 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 Hiroshima water hard or soft?
It is soft: 20 mg/L as CaCO₃ (1.2 gpg, 1.1 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Hiroshima 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 Hiroshima water?
1.2 gpg, equal to 1.1 °dH, 2 °fH or 20 mg/L calcium carbonate.
What dishwasher salt setting should I use in Hiroshima?
For 20 mg/L (1.1 °dH) check your manufacturer's table: level 0–1, usually no salt.
Do I need a water softener in Hiroshima?
No. With soft water a softener adds nothing.
Source
Source: 広島市水道局 Hiroshima City Waterworks Bureau, tap-water quality results by supply system FY2025 (2025). Method: figure published by the water supplier. 広島市水道局 Hiroshima City Waterworks Bureau, tap-water quality results by supply system FY2025 · Outdated figure? Tell us