Water hardness in Iwaki
39 mg/L soft
Tap water in Iwaki is soft: 39 mg/L (2.3 gpg · 2.2 °dH · 3.9 °fH).
Source: Iwaki City Waterworks Bureau, water quality annual report 2025 edition (FY2024 data) (2024) · data checked 2026-10-21
Range across supply zones: 19–60 mg/L.
Iwaki's tap water is supplied by Iwaki City Waterworks Bureau; the intake mix is not confirmed here, but piped water in Fukushima Prefecture comes mainly from rivers and reservoirs fed by short, steep catchments. The utility's 2024 data give 39.0 mg/L CaCO₃ within a range of 19.0 to 60.0 mg/L; the spread is wide, so the value at your tap depends on where in the supply area you live. 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 | 39 mg/L |
|---|---|
| Utility | Iwaki City Waterworks Bureau |
How Iwaki compares
- Tap water in Iwaki is 22 % softer than the median of the 228 cities we track in Japan (50 mg/L).
- By hardness it ranks 175 of 228 in Japan (1 = hardest); 22 % of these cities have softer water.
- In Fukushima it is number 1 of 3 cities; the regional median is 33 mg/L.
- Nearest city with clearly softer water: Fukushima, 86 km away (16 mg/L).
- Nearest city with clearly harder water: Mito, 87 km away (56 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 Iwaki
| 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 Iwaki water hard or soft?
It is soft: 39 mg/L as CaCO₃ (2.3 gpg, 2.2 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Iwaki 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 Iwaki water?
2.3 gpg, equal to 2.2 °dH, 3.9 °fH or 39 mg/L calcium carbonate.
What dishwasher salt setting should I use in Iwaki?
For 39 mg/L (2.2 °dH) check your manufacturer's table: level 0–1, usually no salt.
Do I need a water softener in Iwaki?
No. With soft water a softener adds nothing.
Source
Source: Iwaki City Waterworks Bureau, water quality annual report 2025 edition (FY2024 data) (2024). Method: figure published by the water supplier. Iwaki City Waterworks Bureau, water quality annual report 2025 edition (FY2024 data) · Outdated figure? Tell us