Water hardness in Ota (Gunma)
51 mg/L soft
Tap water in Ota (Gunma) is soft: 51 mg/L (3 gpg · 2.9 °dH · 5.1 °fH).
Source: Gunma Tobu Waterworks Authority (群馬東部水道企業団), tap-water quality results FY2025 (2025) · data checked 2026-10-21
Range across supply zones: 34–86 mg/L.
Ota is served by the Gunma Tobu Waterworks Authority, which receives surface water from the Tone River upstream of the Tone Barrage and from the Watarase River above the Takatsudo Dam; the area has been shifting from groundwater to surface water. The utility's 2025 data give 51.0 mg/L CaCO₃ within a range of 34.0 to 86.0 mg/L; the spread is wide, so the value at your tap depends on where in the supply area you live. Expect gradual white deposits on kettles, taps and showerheads; descaling now and then with citric acid is usually enough.
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 | 51 mg/L |
|---|---|
| Utility | Gunma Tobu Waterworks Authority (群馬東部水道企業団) |
How Ota (Gunma) compares
- Tap water in Ota (Gunma) is close to the median of the 228 cities we track in Japan (50 mg/L).
- By hardness it ranks 113 of 228 in Japan (1 = hardest); 51 % of these cities have softer water.
- In Gunma it is number 6 of 11 cities; the regional median is 51 mg/L.
- Nearest city with clearly softer water: Itakura, 24 km away (41 mg/L).
- Nearest city with clearly harder water: Chiyoda, 12 km away (79 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 Ota
| 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 Ota (Gunma) water hard or soft?
It is soft: 51 mg/L as CaCO₃ (3 gpg, 2.9 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Ota (Gunma) 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 Ota (Gunma) water?
3 gpg, equal to 2.9 °dH, 5.1 °fH or 51 mg/L calcium carbonate.
What dishwasher salt setting should I use in Ota (Gunma)?
For 51 mg/L (2.9 °dH) check your manufacturer's table: level 0–1, usually no salt.
Do I need a water softener in Ota (Gunma)?
No. With soft water a softener adds nothing.
Source
Source: Gunma Tobu Waterworks Authority (群馬東部水道企業団), tap-water quality results FY2025 (2025). Method: figure published by the water supplier. Gunma Tobu Waterworks Authority (群馬東部水道企業団), tap-water quality results FY2025 · Outdated figure? Tell us