Water hardness in Winchester
302 mg/L very hard
Tap water in Winchester is very hard: 302 mg/L (17.6 gpg · 16.9 °dH · 30.2 °fH).
Source: Southern Water — domestic drinking water quality (Stream open data, CC BY) (2026-04) · data checked 2026-10-19
Range across supply zones: 290–312 mg/L.
The supply to Winchester is run by Southern Water, which relies mainly on chalk groundwater across Kent, Sussex, Hampshire and the Isle of Wight. Reported hardness is 302.1 mg/L CaCO₃, ranging from 289.7 to 312.1 mg/L between supply zones. Water from chalk and limestone picks up calcium and magnesium as it percolates, which is why hardness is high; it is hard to very hard water, so scale builds quickly on kettles, showers and heating elements and shortens appliance life unless treated.
UK suppliers report mg/L CaCO₃ and often Clark degrees (1 °Clark = 14.25 mg/L).
Water data
| Total hardness | 302 mg/L |
|---|---|
| Utility | Southern Water |
How Winchester compares
- Tap water in Winchester is 64 % harder than the median of the 471 cities we track in the United Kingdom (185 mg/L).
- By hardness it ranks 57 of 471 in the United Kingdom (1 = hardest); 87 % of these cities have softer water.
- In Winchester it is number 1 of 5 cities; the regional median is 302 mg/L.
- Nearest city with clearly softer water: Netheravon, 38 km away (222 mg/L).
Ranking of the hardest and softest water in the United Kingdom →
What it means at home
- Severe scale: heater elements and washing-machine heaters fail early.
- Detergent use is very high; taps and screens coat within days.
- Dishwasher at maximum salt setting.
- An ion-exchange softener is practically essential; RO for drinking water.
How much salt will you use for softening?
Yes. At this hardness a softener pays for itself through appliance life and detergent.
Descale a coffee machine or kettle about every 1 months (typical manufacturer guidance for this hardness).
Estimates for planning, not a quote. Check your appliance manual for exact settings.
Dishwasher setting in Winchester
| Brand | Setting for this water |
|---|---|
| Bosch | H05 |
| Miele | 17 °dH |
| AEG / Electrolux | 4 |
| Beko | 5th |
| Hoover | S3 |
| LG | H3 |
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 Winchester water hard or soft?
It is very hard: 302 mg/L as CaCO₃ (17.6 gpg, 16.9 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Winchester safe to drink?
Hardness is not a health issue; it is about limescale, taste and appliances. Mains water must meet national drinking-water standards. UK suppliers report mg/L CaCO₃ and often Clark degrees (1 °Clark = 14.25 mg/L).
How many grains per gallon is Winchester water?
17.6 gpg, equal to 16.9 °dH, 30.2 °fH or 302 mg/L calcium carbonate.
What dishwasher salt setting should I use in Winchester?
For 302 mg/L (16.9 °dH) check your manufacturer's table: maximum level (5–7).
Do I need a water softener in Winchester?
Yes, unless you are only passing through: scale damages appliances within a few years.
Source
Source: Southern Water — domestic drinking water quality (Stream open data, CC BY) (2026-04). Method: own measurement. Southern Water — domestic drinking water quality (Stream open data, CC BY) · Outdated figure? Tell us