Water hardness in Nagaoka
35 mg/L soft
Tap water in Nagaoka is soft: 35 mg/L (2 gpg · 2 °dH · 3.5 °fH).
Source: Nagaoka City Waterworks Bureau, tap-water (給水栓) quality results FY2026 (令和8年度) (2026) · data checked 2026-11-05
Range across supply zones: 9–74 mg/L.
Nagaoka's figure comes from the waterworks bureau's FY2026 tap results, covering April to September 2026 only, so it is a partial year and may shift once autumn and winter samples are added. It combines six main supply systems and fourteen small local systems, giving 20 taps; the median is 35 mg/L and readings run from 9 to 74 mg/L. The small systems are separate supplies, so hardness can differ a lot between the central city and outlying districts. Two of the main treatment areas had no hardness values published yet and are not included.
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 | 35 mg/L |
|---|---|
| Utility | Nagaoka City Waterworks Bureau (長岡市水道局) |
How Nagaoka compares
- Tap water in Nagaoka is 30 % softer than the median of the 228 cities we track in Japan (50 mg/L).
- By hardness it ranks 194 of 228 in Japan (1 = hardest); 15 % of these cities have softer water.
- In Niigata it is number 1 of 3 cities; the regional median is 33 mg/L.
- Nearest city with clearly softer water: Niigata, 55 km away (19 mg/L).
- Nearest city with clearly harder water: Nagano, 107 km away (50 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 Nagaoka
| 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 Nagaoka water hard or soft?
It is soft: 35 mg/L as CaCO₃ (2 gpg, 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 Nagaoka 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 Nagaoka water?
2 gpg, equal to 2 °dH, 3.5 °fH or 35 mg/L calcium carbonate.
What dishwasher salt setting should I use in Nagaoka?
For 35 mg/L (2 °dH) check your manufacturer's table: level 0–1, usually no salt.
Do I need a water softener in Nagaoka?
No. With soft water a softener adds nothing.
Source
Source: Nagaoka City Waterworks Bureau, tap-water (給水栓) quality results FY2026 (令和8年度) (2026). Method: figure published by the water supplier. Nagaoka City Waterworks Bureau, tap-water (給水栓) quality results FY2026 (令和8年度) · Outdated figure? Tell us