Water hardness in Yokosuka
62 mg/L moderately hard
Tap water in Yokosuka is moderately hard: 62 mg/L (3.6 gpg · 3.5 °dH · 6.2 °fH).
Source: 横須賀市上下水道局 Yokosuka City Waterworks & Sewerage Bureau, water quality annual report FY2025 (taps) (2025) · data checked 2026-10-21
Range across supply zones: 53–129 mg/L.
Yokosuka takes part of its supply from the Sagami and Sakawa river systems through facilities shared with Kanagawa Prefecture, Yokohama and Kawasaki. The utility's 2025 data give 62.0 mg/L CaCO₃ within a range of 53.0 to 129.0 mg/L. Expect gradual white deposits on kettles, taps and showerheads; descaling now and then with citric acid is usually 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 | 62 mg/L |
|---|---|
| Utility | Yokosuka City Waterworks & Sewerage Bureau |
How Yokosuka compares
- Tap water in Yokosuka is 24 % harder than the median of the 228 cities we track in Japan (50 mg/L).
- By hardness it ranks 70 of 228 in Japan (1 = hardest); 68 % of these cities have softer water.
- In Kanagawa it is number 6 of 12 cities; the regional median is 62 mg/L.
- Nearest city with clearly softer water: Musashi-murayama, 55 km away (48 mg/L).
- Nearest city with clearly harder water: Ichihara, 46 km away (86 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 Yokosuka
| Brand | Setting for this water |
|---|---|
| Bosch | H00 |
| Miele | 3 °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 Yokosuka water hard or soft?
It is moderately hard: 62 mg/L as CaCO₃ (3.6 gpg, 3.5 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Yokosuka 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 Yokosuka water?
3.6 gpg, equal to 3.5 °dH, 6.2 °fH or 62 mg/L calcium carbonate.
What dishwasher salt setting should I use in Yokosuka?
For 62 mg/L (3.5 °dH) check your manufacturer's table: level 2–3.
Do I need a water softener in Yokosuka?
Not essential; a scale inhibitor protects the heater cheaply.
Source
Source: 横須賀市上下水道局 Yokosuka City Waterworks & Sewerage Bureau, water quality annual report FY2025 (taps) (2025). Method: figure published by the water supplier. 横須賀市上下水道局 Yokosuka City Waterworks & Sewerage Bureau, water quality annual report FY2025 (taps) · Outdated figure? Tell us