Water hardness in Koshigaya
61 mg/L moderately hard
Tap water in Koshigaya is moderately hard: 61 mg/L (3.6 gpg · 3.4 °dH · 6.1 °fH).
Source: Koshigaya-Matsubushi Water Supply Authority, tap-water quality annual results FY2025 (令和7年度 給水栓水質検査結果年報) (2025) · data checked 2026-10-21
Range across supply zones: 45–80 mg/L.
Koshigaya sits in the part of Saitama where Tone and Arakawa river water treated by the prefecture is the main supply, with some cities adding their own wells; the exact mix for Koshigaya is not confirmed here. The reported figure is 61.2 mg/L CaCO₃ (range 44.7 to 80.2 mg/L, 2025 data). 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 | 61 mg/L |
|---|---|
| Utility | Koshigaya-Matsubushi Water Supply Authority (越谷・松伏水道企業団) |
How Koshigaya compares
- Tap water in Koshigaya is 22 % harder than the median of the 228 cities we track in Japan (50 mg/L).
- By hardness it ranks 75 of 228 in Japan (1 = hardest); 67 % of these cities have softer water.
- In Saitama it is number 8 of 9 cities; the regional median is 67 mg/L.
- Nearest city with clearly softer water: Higashiyamato, 36 km away (48 mg/L).
- Nearest city with clearly harder water: Musashino, 29 km away (82 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 Koshigaya
| 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 Koshigaya water hard or soft?
It is moderately hard: 61 mg/L as CaCO₃ (3.6 gpg, 3.4 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Koshigaya 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 Koshigaya water?
3.6 gpg, equal to 3.4 °dH, 6.1 °fH or 61 mg/L calcium carbonate.
What dishwasher salt setting should I use in Koshigaya?
For 61 mg/L (3.4 °dH) check your manufacturer's table: level 2–3.
Do I need a water softener in Koshigaya?
Not essential; a scale inhibitor protects the heater cheaply.
Source
Source: Koshigaya-Matsubushi Water Supply Authority, tap-water quality annual results FY2025 (令和7年度 給水栓水質検査結果年報) (2025). Method: figure published by the water supplier. Koshigaya-Matsubushi Water Supply Authority, tap-water quality annual results FY2025 (令和7年度 給水栓水質検査結果年報) · Outdated figure? Tell us