Water hardness in Tsukuba
82 mg/L moderately hard
Tap water in Tsukuba is moderately hard: 82 mg/L (4.8 gpg · 4.6 °dH · 8.2 °fH).
Source: City of Tsukuba Waterworks, water quality test results FY2025 (令和7年度 水質検査結果書) (2025) · data checked 2026-11-05
Range across supply zones: 74–88 mg/L.
The city's FY2025 results come from six district sampling sites (Tsukuba, Toyosato, Oho, Sakura, Yatabe, Kukizaki), each tested four times in the year. Site averages are all close, and the 82 mg/L shown is their median, with readings between 73.7 and 88.2 mg/L. That is the highest figure among the newly added cities in this batch, so limescale on kettles and showerheads is likely to show up sooner than in neighbouring Ibaraki cities such as Mito. The results do not name the sources of the supply.
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 | 82 mg/L |
|---|---|
| Utility | つくば市 水道（上下水道局）City of Tsukuba Waterworks |
How Tsukuba compares
- Tap water in Tsukuba is 63 % harder than the median of the 228 cities we track in Japan (50 mg/L).
- By hardness it ranks 9 of 228 in Japan (1 = hardest); 96 % of these cities have softer water.
- In Ibaraki it is number 1 of 3 cities; the regional median is 56 mg/L.
- Nearest city with clearly softer water: Kashiwa, 28 km away (65 mg/L).
- Nearest city with clearly harder water: Hakone, 140 km away (110 mg/L).
Ranking of the hardest and softest water in Japan →
What it means at home
- Visible kettle scale every few weeks; vinegar or citric acid is enough.
- Water heater and washing machine: some long-term scale; a scale inhibitor slows it.
- Dishwasher: medium salt setting.
- Softener optional; pays off mainly with a gas boiler or tankless heater.
How much salt will you use for softening?
Optional. A scale inhibitor or a small softener protects the heater; soap savings are modest.
Descale a coffee machine or kettle about every 3 months (typical manufacturer guidance for this hardness).
Estimates for planning, not a quote. Check your appliance manual for exact settings.
Dishwasher setting in Tsukuba
| Brand | Setting for this water |
|---|---|
| Bosch | H00 |
| Miele | 5 °dH |
| AEG / Electrolux | 2 |
| Beko | 1st |
| Hoover | S1 |
| LG | H1 |
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 Tsukuba water hard or soft?
It is moderately hard: 82 mg/L as CaCO₃ (4.8 gpg, 4.6 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Tsukuba 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 Tsukuba water?
4.8 gpg, equal to 4.6 °dH, 8.2 °fH or 82 mg/L calcium carbonate.
What dishwasher salt setting should I use in Tsukuba?
For 82 mg/L (4.6 °dH) check your manufacturer's table: level 2–3.
Do I need a water softener in Tsukuba?
Not essential; a scale inhibitor protects the heater cheaply.
Source
Source: City of Tsukuba Waterworks, water quality test results FY2025 (令和7年度 水質検査結果書) (2025). Method: figure published by the water supplier. City of Tsukuba Waterworks, water quality test results FY2025 (令和7年度 水質検査結果書) · Outdated figure? Tell us