Water hardness in Devizes
354 mg/L very hard
Tap water in Devizes is very hard: 354 mg/L (20.7 gpg · 19.8 °dH · 35.4 °fH).
Source: Wessex Water — domestic drinking water quality (Stream open data, CC BY) (2025-12) · data checked 2026-10-19
Range across supply zones: 336–365 mg/L.
Wessex Water supplies Devizes; most of the company's water is groundwater from chalk, limestone and sandstone aquifers, with around a fifth from Somerset reservoirs. Reported hardness is 354.0 mg/L CaCO₃, ranging from 335.6 to 365.0 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 | 354 mg/L |
|---|---|
| Utility | Wessex Water |
How Devizes compares
- Tap water in Devizes is 92 % harder than the median of the 471 cities we track in the United Kingdom (185 mg/L).
- By hardness it ranks 11 of 471 in the United Kingdom (1 = hardest); 98 % of these cities have softer water.
- In Wiltshire it is number 6 of 34 cities; the regional median is 304 mg/L.
- Nearest city with clearly softer water: Bratton, 13 km away (280 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 Devizes
| Brand | Setting for this water |
|---|---|
| Bosch | H05 |
| Miele | 20 °dH |
| AEG / Electrolux | 5 |
| Beko | 6th |
| 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 Devizes water hard or soft?
It is very hard: 354 mg/L as CaCO₃ (20.7 gpg, 19.8 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Devizes 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 Devizes water?
20.7 gpg, equal to 19.8 °dH, 35.4 °fH or 354 mg/L calcium carbonate.
What dishwasher salt setting should I use in Devizes?
For 354 mg/L (19.8 °dH) check your manufacturer's table: maximum level (5–7).
Do I need a water softener in Devizes?
Yes, unless you are only passing through: scale damages appliances within a few years.
Source
Source: Wessex Water — domestic drinking water quality (Stream open data, CC BY) (2025-12). Method: own measurement. Wessex Water — domestic drinking water quality (Stream open data, CC BY) · Outdated figure? Tell us