Water hardness in Osaka
42 mg/L soft
Tap water in Osaka is soft: 42 mg/L (2.5 gpg · 2.4 °dH · 4.2 °fH).
Source: Osaka City Waterworks Bureau, water quality results by sampling point 2025-08 to 2026-07 (2026) · data checked 2026-10-21
Range across supply zones: 41–42 mg/L.
Osaka's supply depends entirely on the Yodo River, which carries the outflow of Lake Biwa and is treated at the Kunijima, Niwakubo and Toyono plants. The utility's 2026 data give 42.0 mg/L CaCO₃ within a range of 41.0 to 42.0 mg/L. Scale builds slowly at this level; a light white film on kettles and taps is possible, and a softener is rarely needed.
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 | 42 mg/L |
|---|---|
| Utility | Osaka City Waterworks Bureau |
How Osaka compares
- Tap water in Osaka is 16 % softer than the median of the 228 cities we track in Japan (50 mg/L).
- By hardness it ranks 150 of 228 in Japan (1 = hardest); 30 % of these cities have softer water.
- In Osaka it is number 21 of 42 cities; the regional median is 42 mg/L.
- Nearest city with clearly softer water: Tondabayashi, 23 km away (17 mg/L).
- Nearest city with clearly harder water: Settsu, 13 km away (63 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 Osaka
| 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 Osaka water hard or soft?
It is soft: 42 mg/L as CaCO₃ (2.5 gpg, 2.4 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Osaka 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 Osaka water?
2.5 gpg, equal to 2.4 °dH, 4.2 °fH or 42 mg/L calcium carbonate.
What dishwasher salt setting should I use in Osaka?
For 42 mg/L (2.4 °dH) check your manufacturer's table: level 0–1, usually no salt.
Do I need a water softener in Osaka?
No. With soft water a softener adds nothing.
Source
Source: Osaka City Waterworks Bureau, water quality results by sampling point 2025-08 to 2026-07 (2026). Method: figure published by the water supplier. Osaka City Waterworks Bureau, water quality results by sampling point 2025-08 to 2026-07 · Outdated figure? Tell us