Water hardness in Koriyama
33 mg/L soft
Tap water in Koriyama is soft: 33 mg/L (2 gpg · 1.9 °dH · 3.3 °fH).
Source: 郡山市上下水道局 Koriyama City Waterworks and Sewerage Bureau, monthly tap-water quality results FY2025 (2025) · data checked 2026-10-21
Range across supply zones: 16–67 mg/L.
Koriyama gets most of its water from Lake Inawashiro, with the Miharu Dam, the Ose and Fukasawa rivers and springs as the other sources. Hardness is reported at 33.4 mg/L CaCO₃, ranging from 15.5 to 67.0 mg/L (2025 data); the spread is wide, so the value at your tap depends on where in the supply area you live. Limescale is mild here, appearing slowly on kettles and taps, so occasional descaling is 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 | 33 mg/L |
|---|---|
| Utility | Koriyama City Waterworks and Sewerage Bureau |
How Koriyama compares
- Tap water in Koriyama is 33 % softer than the median of the 228 cities we track in Japan (50 mg/L).
- By hardness it ranks 200 of 228 in Japan (1 = hardest); 12 % of these cities have softer water.
- In Fukushima it is number 2 of 3 cities; the regional median is 33 mg/L.
- Nearest city with clearly softer water: Fukushima, 40 km away (16 mg/L).
- Nearest city with clearly harder water: Mito, 117 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 Koriyama
| 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 Koriyama water hard or soft?
It is soft: 33 mg/L as CaCO₃ (2 gpg, 1.9 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Koriyama 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 Koriyama water?
2 gpg, equal to 1.9 °dH, 3.3 °fH or 33 mg/L calcium carbonate.
What dishwasher salt setting should I use in Koriyama?
For 33 mg/L (1.9 °dH) check your manufacturer's table: level 0–1, usually no salt.
Do I need a water softener in Koriyama?
No. With soft water a softener adds nothing.
Source
Source: 郡山市上下水道局 Koriyama City Waterworks and Sewerage Bureau, monthly tap-water quality results FY2025 (2025). Method: figure published by the water supplier. 郡山市上下水道局 Koriyama City Waterworks and Sewerage Bureau, monthly tap-water quality results FY2025 · Outdated figure? Tell us