Water hardness in Mitoyo
71 mg/L moderately hard
Tap water in Mitoyo is moderately hard: 71 mg/L (4.1 gpg · 4 °dH · 7.1 °fH).
Source: Kagawa Prefectural Wide-Area Waterworks Authority (香川県広域水道企業団), tap-water quality results FY2025 (2025) · data checked 2026-10-21
Range across supply zones: 23–102 mg/L.
Mitoyo is served by the Kagawa Prefectural Wide-Area Waterworks Authority; about half of Kagawa's tap water depends on the Kagawa Canal, which carries Yoshino River water from the Sameura and Ikeda dams, with in-prefecture sources supplying the rest. The utility's 2025 data give 71.0 mg/L CaCO₃ within a range of 23.0 to 102.0 mg/L; the spread is wide, so the value at your tap depends on where in the supply area you live. Deposits form on kettles, heaters and showerheads fairly quickly at this level, so regular descaling matters.
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 | 71 mg/L |
|---|---|
| Utility | Kagawa Prefectural Wide-Area Waterworks Authority (香川県広域水道企業団) |
How Mitoyo compares
- Tap water in Mitoyo is 41 % harder than the median of the 228 cities we track in Japan (50 mg/L).
- By hardness it ranks 24 of 228 in Japan (1 = hardest); 89 % of these cities have softer water.
- In Kagawa it is number 2 of 16 cities; the regional median is 46 mg/L.
- Nearest city with clearly softer water: Kan'onji, 10 km away (39 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 Mitoyo
| Brand | Setting for this water |
|---|---|
| Bosch | H00 |
| Miele | 4 °dH |
| AEG / Electrolux | 2 |
| Beko | 1st |
| 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 Mitoyo water hard or soft?
It is moderately hard: 71 mg/L as CaCO₃ (4.1 gpg, 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 Mitoyo 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 Mitoyo water?
4.1 gpg, equal to 4 °dH, 7.1 °fH or 71 mg/L calcium carbonate.
What dishwasher salt setting should I use in Mitoyo?
For 71 mg/L (4 °dH) check your manufacturer's table: level 2–3.
Do I need a water softener in Mitoyo?
Not essential; a scale inhibitor protects the heater cheaply.
Source
Source: Kagawa Prefectural Wide-Area Waterworks Authority (香川県広域水道企業団), tap-water quality results FY2025 (2025). Method: figure published by the water supplier. Kagawa Prefectural Wide-Area Waterworks Authority (香川県広域水道企業団), tap-water quality results FY2025 · Outdated figure? Tell us