Water hardness in Sennan
42 mg/L soft
Tap water in Sennan is soft: 42 mg/L (2.5 gpg · 2.4 °dH · 4.2 °fH).
Source: Osaka Water Supply Authority, Sennan water service (大阪広域水道企業団 泉南水道事業), via Osaka Prefecture 「大阪府の水道の現況」 FY2024 water quality tables (2024) · data checked 2026-10-21
Range across supply zones: 41–42 mg/L.
Sennan's water service is run by the Osaka Water Supply Authority, whose supply is Yodo River water treated at its Murano, Niwakubo and Mishima plants; local sources may also contribute, which is not confirmed here. Hardness is reported at 42.0 mg/L CaCO₃, ranging from 41.0 to 42.0 mg/L (2024 data). Scale builds slowly at this level; a light white film on kettles and taps is possible, and a softener is rarely needed.
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 | 42 mg/L |
|---|---|
| Utility | Osaka Water Supply Authority, Sennan water service (大阪広域水道企業団 泉南水道事業) |
How Sennan compares
- Tap water in Sennan is 16 % softer than the median of the 228 cities we track in Japan (50 mg/L).
- By hardness it ranks 150 of 228 in Japan (1 = hardest); 30 % of these cities have softer water.
- In Osaka it is number 21 of 42 cities; the regional median is 42 mg/L.
- Nearest city with clearly softer water: Misaki, 12 km away (31 mg/L).
- Nearest city with clearly harder water: Izumisano, 6 km away (54 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 Sennan
| 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 Sennan water hard or soft?
It is soft: 42 mg/L as CaCO₃ (2.5 gpg, 2.4 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Sennan 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 Sennan water?
2.5 gpg, equal to 2.4 °dH, 4.2 °fH or 42 mg/L calcium carbonate.
What dishwasher salt setting should I use in Sennan?
For 42 mg/L (2.4 °dH) check your manufacturer's table: level 0–1, usually no salt.
Do I need a water softener in Sennan?
No. With soft water a softener adds nothing.
Source
Source: Osaka Water Supply Authority, Sennan water service (大阪広域水道企業団 泉南水道事業), via Osaka Prefecture 「大阪府の水道の現況」 FY2024 water quality tables (2024). Method: figure published by the water supplier. Osaka Water Supply Authority, Sennan water service (大阪広域水道企業団 泉南水道事業), via Osaka Prefecture 「大阪府の水道の現況」 FY2024 water quality tables · Outdated figure? Tell us