Water hardness in Castlereagh
65 mg/L moderately hard
Tap water in Castlereagh is moderately hard: 65 mg/L (3.8 gpg · 3.6 °dH · 6.5 °fH).
Source: NI Water, customer tap results 2024,2025 (OpenDataNI, OGL v3.0) (2025-12) · data checked 2026-10-19
Range across supply zones: 39–69 mg/L.
NI Water supplies Castlereagh; the company uses 39 sources, nearly all surface water from loughs, rivers and reservoirs, and only a tiny share from boreholes. Reported hardness is 64.9 mg/L CaCO₃, ranging from 39.2 to 68.7 mg/L between supply zones. Hardness varies with the catchment each treatment works draws from; it sits in the moderately hard band, where limescale appears on kettles and shower heads over months and dishwasher salt helps.
UK suppliers report mg/L CaCO₃ and often Clark degrees (1 °Clark = 14.25 mg/L).
Water data
| Total hardness | 65 mg/L |
|---|---|
| Utility | Northern Ireland Water |
How Castlereagh compares
- Tap water in Castlereagh is 65 % softer than the median of the 471 cities we track in the United Kingdom (185 mg/L).
- By hardness it ranks 368 of 471 in the United Kingdom (1 = hardest); 22 % of these cities have softer water.
- In Northern Ireland it is number 77 of 110 cities; the regional median is 100 mg/L.
- Nearest city with clearly softer water: Carryduff, 6 km away (23 mg/L).
- Nearest city with clearly harder water: Newtownabbey, 10 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 Castlereagh
| Brand | Setting for this water |
|---|---|
| Bosch | H00 |
| Miele | 4 °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 Castlereagh water hard or soft?
It is moderately hard: 65 mg/L as CaCO₃ (3.8 gpg, 3.6 °dH). The usual bands are soft < 60, moderately hard 60–120, hard 120–180 and very hard > 180 mg/L.
Is tap water in Castlereagh 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 Castlereagh water?
3.8 gpg, equal to 3.6 °dH, 6.5 °fH or 65 mg/L calcium carbonate.
What dishwasher salt setting should I use in Castlereagh?
For 65 mg/L (3.6 °dH) check your manufacturer's table: level 2–3.
Do I need a water softener in Castlereagh?
Not essential; a scale inhibitor protects the heater cheaply.
Source
Source: NI Water, customer tap results 2024,2025 (OpenDataNI, OGL v3.0) (2025-12). Method: own measurement. NI Water, customer tap results 2024,2025 (OpenDataNI, OGL v3.0) · Outdated figure? Tell us