Water hardness in Belfast
75 mg/L moderately hard
Tap water in Belfast is moderately hard: 75 mg/L (4.4 gpg · 4.2 °dH · 7.5 °fH).
Source: NI Water - Water Hardness by Water Supply Zone 2025 (OpenDataNI, OGL) (2025) · data checked 2026-10-19
Range across supply zones: 43–158 mg/L.
6 supply zones — hardness varies by neighbourhood; the figure above is the median.
Hardness by district / supply zone
| mg/L | mg/L | ||
|---|---|---|---|
| ZS0103 Belfast Ballyhanwood | 43 | 43 | soft |
| ZS0104 Belfast Breda North | 82 | 82 | moderately hard |
| ZS0105 Belfast Breda South | 67 | 67 | moderately hard |
| ZS0106 Dunore Belfast North | 157 | 157 | hard |
| ZS0107 Belfast Oldpark | 158 | 158 | hard |
| ZS0108 Belfast Purdysburn | 55 | 55 | soft |
Belfast is supplied by NI Water, which reports total hardness for six Belfast-named water supply zones in its 2025 zone table. The median is 74.6 mg/L CaCO₃ and the range is 43.1 to 157.7 mg/L, so the figure depends on which zone your street falls in. The Dunore and Oldpark zones sit at the harder end; the underlying sources for each zone are not confirmed here, so check your postcode in NI Water's postcode-to-zone file before choosing a softener.
UK suppliers report mg/L CaCO₃ and often Clark degrees (1 °Clark = 14.25 mg/L).
Water data
| Total hardness | 75 mg/L |
|---|---|
| Utility | NI Water |
How Belfast compares
- Tap water in Belfast is 60 % softer than the median of the 471 cities we track in the United Kingdom (185 mg/L).
- By hardness it ranks 355 of 471 in the United Kingdom (1 = hardest); 25 % of these cities have softer water.
- Nearest city with clearly softer water: Holywood, 8 km away (31 mg/L).
- Nearest city with clearly harder water: Newtownabbey, 7 km away (147 mg/L).
Ranking of the hardest and softest water in the United Kingdom →
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 Belfast
| Brand | Setting for this water |
|---|---|
| Bosch | H00 |
| Miele | 4 °dH |
| AEG / Electrolux | 2 |
| Beko | 1st |
| Hoover | S1 |
| LG | H1 |
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 Belfast water hard or soft?
It is moderately hard: 75 mg/L as CaCO₃ (4.4 gpg, 4.2 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Belfast 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 Belfast water?
4.4 gpg, equal to 4.2 °dH, 7.5 °fH or 75 mg/L calcium carbonate.
What dishwasher salt setting should I use in Belfast?
For 75 mg/L (4.2 °dH) check your manufacturer's table: level 2–3.
Do I need a water softener in Belfast?
Not essential; a scale inhibitor protects the heater cheaply.
Source
Source: NI Water - Water Hardness by Water Supply Zone 2025 (OpenDataNI, OGL) (2025). Method: figure published by the water supplier. NI Water - Water Hardness by Water Supply Zone 2025 (OpenDataNI, OGL) · Outdated figure? Tell us