Castlereagh Water Hardness & Quality Report (2026)
Water Hardness
7.7°Clark11°fH6.2°dH
Source
reservoir
pH Level
7.7
neutral = 7.0
Lead
0.004 mg/L
✓ Below action level
TDS
231.5 mg/L
Est. Daily Cost
£0.25
energy & soap waste
Source: DWI Data Portal · Updated 2026
0–60
mg/L
Soft
61–120
mg/L
Moderately Hard
121–180
mg/L
Hard
180+
mg/L
Very Hard
Appliance Damage Report
In Castlereagh, your appliances are currently losing 15% efficiency due to mineral buildup.
| Appliance | In Castlereagh | Soft Water City | Efficiency Loss |
|---|---|---|---|
| Kettle | 6 yrs | 8.5 yrs | -29% |
| Washing Machine | 9.5 yrs | 12 yrs | -21% |
| Water Heater | 11.2 yrs | 15 yrs | -25% |
Regional Water Comparison
How Castlereagh compares to its nearest neighbours
| City | Hardness | Clark° | Risk | Source |
|---|---|---|---|---|
| ▶ Castlereagh, Northern Ireland | 110 mg/L | 7.7° | 🟡 Moderately Hard | reservoir |
| Belfast, Northern Ireland | 70 mg/L | 4.9° | 🟡 Moderately Hard | reservoir |
| Holywood, Northern Ireland | 154.5 mg/L | 10.8° | 🟠 Hard | reservoir |
| Dundonald, Northern Ireland | 98 mg/L | 6.9° | 🟡 Moderately Hard | reservoir |
| Newtownabbey, Northern Ireland | 155 mg/L | 10.9° | 🟠 Hard | reservoir |
National Benchmark
How Castlereagh compares to the United Kingdom average
| Benchmark | Hardness | Appliance Risk |
|---|---|---|
| ▶ Castlereagh | 110 mg/L | 🟡 Low |
| United Kingdom National Avg | 183 mg/L | 🔴 High |
| Livingston Top Rated | 8.5 mg/L | 🟢 None |
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What Makes Castlereagh's Water Unique?
Local geology and source profile
Castlereagh, the east Belfast suburb in the greater Belfast area of County Down, is supplied by NI Water from the Silent Valley and Ben Crom Reservoirs in the Mourne Mountains of south Down. NI Water conveys Mourne Mountain supply northward via the Silent Valley aqueduct to the Belfast metropolitan area. Castlereagh and the east Belfast suburbs receive this Mourne supply through the Greater Belfast distribution network, which traverses the drumlin-covered landscape of County Down between the Mournes and Belfast Lough. The Mourne Granites catchment yields exceptionally soft water, but the distribution network passing through the drumlin country — underlain by Silurian greywacke and glacial till — picks up a modest calcium increment from the geology and distribution infrastructure.
Castlereagh's hardness of 110 mg/L (7.7°Clark) is somewhat above the pure Mourne granite baseline (~40 mg/L), reflecting distribution network contributions and the modest calcium from the County Down drumlin landscape. The Silurian greywacke and glacial till of the east Down drumlin field contribute minor dissolved calcium to the supply as water travels northward from the Mournes through the distribution network. The Drinking Water Quality Regulator for Northern Ireland classifies this as moderately soft.
Limescale is a moderate concern in Castlereagh. At 110 mg/L, limescale forms gradually — kettles need descaling every one to two months. Combi-boiler heat exchangers accumulate modest deposits; annual servicing is sensible. Showerheads and taps develop light deposits. Washing-up liquid lathers reasonably well. Adding Calgon monthly to the washing machine and a periodic kettle descale is adequate limescale management for most Castlereagh households.
Geology & Source: Supplied by NI Water from Silent Valley and Ben Crom Reservoirs in the Mourne Mountains — Castlereagh's east Belfast position draws on NI Water's Mourne granite reservoir supply, with moderate mineral increments from the distribution network traversing east Belfast's drumlin and glacial till landscape, producing moderately soft water at 110 mg/L (7.7°Clark).