Water hardness in Toyokawa
30 mg/L soft
Tap water in Toyokawa is soft: 30 mg/L (1.8 gpg · 1.7 °dH · 3 °fH).
Source: 豊川市上下水道部水道整備課 水質検査結果 令和7年度 (r7kennsakekka.pdf) (2025) · data checked 2026-11-07
Range across supply zones: 16–84 mg/L.
11 supply zones — hardness varies by neighbourhood; the figure above is the median.
Hardness by district / supply zone
| mg/L | mg/L | ||
|---|---|---|---|
| 一宮浄水場(一宮配水池)系統 (Ichinomiya WTP, Ichinomiya reservoir system) | 81 | 81 | moderately hard |
| 一宮浄水場(千両配水池)系統 (Ichinomiya WTP, Senryo reservoir system) | 40 | 40 | soft |
| 中山配水池系統 (Nakayama reservoir system) | 21 | 21 | soft |
| 小坂井配水場系統 (Kosakai WTP system) | 30 | 30 | soft |
| 平尾第１配水池系統 (Hirao No.1 reservoir system) | 20 | 20 | soft |
| 御馬浄水場系統 (Goma WTP system) | 40 | 40 | soft |
| 権現送水場系統 (Gongen pumping station system) | 25 | 25 | soft |
| 権現配水池系統 (Gongen reservoir system) | 25 | 25 | soft |
| 為当水源配水場系統 (Tameto WTP system) | 57 | 57 | soft |
| 豊沢配水池系統 (Hozawa reservoir system) | 23 | 23 | soft |
| 赤坂水源浄水場系統 (Akasaka WTP system) | 30 | 30 | soft |
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 | 30 mg/L |
|---|---|
| Utility | 豊川市上下水道部水道整備課 Toyokawa City Water Supply Division |
How Toyokawa compares
- Tap water in Toyokawa is 40 % softer than the median of the 228 cities we track in Japan (50 mg/L).
- By hardness it ranks 207 of 228 in Japan (1 = hardest); 9 % of these cities have softer water.
- In Aichi it is number 3 of 8 cities; the regional median is 20 mg/L.
- Nearest city with clearly softer water: Okazaki, 26 km away (19 mg/L).
- Nearest city with clearly harder water: Toyohashi, 6 km away (48 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 Toyokawa
| Brand | Setting for this water |
|---|---|
| Bosch | H00 |
| Miele | 2 °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 Toyokawa water hard or soft?
It is soft: 30 mg/L as CaCO₃ (1.8 gpg, 1.7 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Toyokawa 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 Toyokawa water?
1.8 gpg, equal to 1.7 °dH, 3 °fH or 30 mg/L calcium carbonate.
What dishwasher salt setting should I use in Toyokawa?
For 30 mg/L (1.7 °dH) check your manufacturer's table: level 0–1, usually no salt.
Do I need a water softener in Toyokawa?
No. With soft water a softener adds nothing.
Source
Source: 豊川市上下水道部水道整備課 水質検査結果 令和7年度 (r7kennsakekka.pdf) (2025). Method: figure published by the water supplier. 豊川市上下水道部水道整備課 水質検査結果 令和7年度 (r7kennsakekka.pdf) · Outdated figure? Tell us