Water hardness in Ayagawa
77 mg/L moderately hard
Tap water in Ayagawa is moderately hard: 77 mg/L (4.5 gpg · 4.3 °dH · 7.7 °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: 61–96 mg/L.
Ayagawa 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. Hardness is reported at 76.8 mg/L CaCO₃, ranging from 61.0 to 96.0 mg/L (2025 data). 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 | 77 mg/L |
|---|---|
| Utility | Kagawa Prefectural Wide-Area Waterworks Authority (香川県広域水道企業団) |
How Ayagawa compares
- Tap water in Ayagawa is 53 % harder than the median of the 228 cities we track in Japan (50 mg/L).
- By hardness it ranks 14 of 228 in Japan (1 = hardest); 94 % of these cities have softer water.
- In Kagawa it is number 1 of 16 cities; the regional median is 46 mg/L.
- Nearest city with clearly softer water: Manno, 9 km away (46 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 Ayagawa
| 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 Ayagawa water hard or soft?
It is moderately hard: 77 mg/L as CaCO₃ (4.5 gpg, 4.3 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Ayagawa 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 Ayagawa water?
4.5 gpg, equal to 4.3 °dH, 7.7 °fH or 77 mg/L calcium carbonate.
What dishwasher salt setting should I use in Ayagawa?
For 77 mg/L (4.3 °dH) check your manufacturer's table: level 2–3.
Do I need a water softener in Ayagawa?
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