Water hardness in Sendai
25 mg/L soft
Tap water in Sendai is soft: 25 mg/L (1.5 gpg · 1.4 °dH · 2.5 °fH).
Source: 仙台市水道局 Sendai City Waterworks Bureau, tap-water quality results FY2025 (2025) · data checked 2026-10-21
Range across supply zones: 13–46 mg/L.
Sendai's supply comes from dams in the Natori, Hirose and Nanakita river basins, such as Ōkura and Kamafusa, plus water bought from Miyagi Prefecture's regional system fed by the Shichikashuku Dam. The utility's 2025 data give 24.9 mg/L CaCO₃ within a range of 13.4 to 45.5 mg/L; 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 | 25 mg/L |
|---|---|
| Utility | Sendai City Waterworks Bureau |
How Sendai compares
- Tap water in Sendai is 50 % softer than the median of the 228 cities we track in Japan (50 mg/L).
- By hardness it ranks 212 of 228 in Japan (1 = hardest); 7 % of these cities have softer water.
- Nearest city with clearly softer water: Fukushima, 67 km away (16 mg/L).
- Nearest city with clearly harder water: Koriyama, 105 km away (33 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 Sendai
| 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 Sendai 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 Sendai 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 Sendai 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 Sendai?
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 Sendai?
No. With soft water a softener adds nothing.
Source
Source: 仙台市水道局 Sendai City Waterworks Bureau, tap-water quality results FY2025 (2025). Method: figure published by the water supplier. 仙台市水道局 Sendai City Waterworks Bureau, tap-water quality results FY2025 · Outdated figure? Tell us