Water hardness in Numazu
38 mg/L soft
Tap water in Numazu is soft: 38 mg/L (2.2 gpg · 2.1 °dH · 3.8 °fH).
Source: Numazu City Waterworks, FY2025 (令和7年度) tap water test results, izumi.pdf (2026-05) · data checked 2026-11-07
Range across supply zones: 24–72 mg/L.
19 supply zones — hardness varies by neighbourhood; the figure above is the median.
Hardness by district / supply zone
| mg/L | mg/L | ||
|---|---|---|---|
| 井出水源配水区域 (Ide) | 48 | 48 | soft |
| 井田配水区域 (Ita) | 59 | 59 | soft |
| 内浦水源配水区域 (Uchiura) | 31 | 31 | soft |
| 北小林水源配水区域 (Kitakobayashi) | 47 | 47 | soft |
| 原水源配水区域 (Hara) | 33 | 33 | soft |
| 古宇水源配水区域 (Kou) | 25 | 25 | soft |
| 新田配水区域 (Heda, Nitta) | 31 | 31 | soft |
| 木瀬川水源配水区域 (Kisegawa) | 47 | 47 | soft |
| 柳沢水源配水区域 (Yanagisawa) | 48 | 48 | soft |
| 江梨水源配水区域 (Enashi) | 54 | 54 | soft |
| 沢田水源配水区域 (Sawada) | 29 | 29 | soft |
| 河内水源配水区域 (Kouchi) | 30 | 30 | soft |
| 泉水源配水区域（八重系）(Izumi, Yae system) | 46 | 46 | soft |
| 泉水源配水区域（岡宮系）(Izumi, Okamiya system) | 47 | 47 | soft |
| 石川水源配水区域 (Ishikawa) | 65 | 65 | moderately hard |
| 足高水源配水区域 (Ashitaka) | 38 | 38 | soft |
| 達磨橋配水区域（舟山系）(Heda, Funayama system) | 34 | 34 | soft |
| 達磨橋配水区域（達磨橋系）(Heda, Darumabashi system) | 30 | 30 | soft |
| 青野水源配水区域 (Oono) | 32 | 32 | soft |
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 | 38 mg/L |
|---|---|
| Utility | 沼津市水道部 Numazu City Waterworks Department |
How Numazu compares
- Tap water in Numazu is 25 % softer than the median of the 228 cities we track in Japan (50 mg/L).
- By hardness it ranks 182 of 228 in Japan (1 = hardest); 20 % of these cities have softer water.
- In Shizuoka it is number 4 of 4 cities; the regional median is 46 mg/L.
- Nearest city with clearly softer water: Kofu, 69 km away (18 mg/L).
- Nearest city with clearly harder water: Fuji, 18 km away (47 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 Numazu
| 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 Numazu water hard or soft?
It is soft: 38 mg/L as CaCO₃ (2.2 gpg, 2.1 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Numazu 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 Numazu water?
2.2 gpg, equal to 2.1 °dH, 3.8 °fH or 38 mg/L calcium carbonate.
What dishwasher salt setting should I use in Numazu?
For 38 mg/L (2.1 °dH) check your manufacturer's table: level 0–1, usually no salt.
Do I need a water softener in Numazu?
No. With soft water a softener adds nothing.
Source
Source: Numazu City Waterworks, FY2025 (令和7年度) tap water test results, izumi.pdf (2026-05). Method: figure published by the water supplier. Numazu City Waterworks, FY2025 (令和7年度) tap water test results, izumi.pdf · Outdated figure? Tell us