Armagh Water Hardness & Quality Report (2026)

Northern Ireland Water supplies Armagh, the ancient ecclesiastical capital of Ireland and home to two cathedrals of St Patrick, from Cam Lough Reservoir in the Ring of Gullion uplands south of Slieve Gullion in south Armagh, treated at Cam Lough Water Treatment Works before distribution across the Armagh city area. At 158 mg/L (11.1°Clark), Armagh's water is moderately hard, reflecting a blend where the upland reservoir supply from the Silurian and Ordovician rock catchment of the Ring of Gullion is influenced by the Carboniferous Limestone and Devonian Old Red Sandstone geology of south Armagh and the drumlin belt to the north.

The Ring of Gullion — a spectacular ring dyke complex in south Armagh — provides the catchment for Cam Lough, draining ancient Silurian greywacke, granodiorite, and Lower Palaeozoic metamorphic rocks of the Caledonian fold belt. South Armagh additionally overlies Carboniferous Limestone along the Cavan–Louth border zone, and the drumlin belt of central Ulster is underlain by glacial till containing limestone erratics that contribute calcium to groundwater and streams. This complex geology produces the moderately hard 158 mg/L supply with TDS 377.6 mg/L that is characteristic of the Armagh city supply.

At 158 mg/L, limescale is a noticeable domestic concern in Armagh. Kettles benefit from descaling every four to six weeks. The combi-boiler should be fitted with a scale inhibitor and serviced annually. Washing-up liquid requires more product than in softer areas. Taps and shower heads develop moderate limescale deposits within two to three weeks; a monthly wipe with white vinegar keeps fixtures clean. The moderately hard supply characterises the south Ulster drumlin belt cities and contrasts with the softer water found in areas of Northern Ireland that draw directly from the Mourne Mountains granite catchment.