Nelson Water Hardness & Quality Report (2026)

Dŵr Cymru Welsh Water supplies Nelson, a village in the Rhymney Valley in Caerphilly County Borough — situated between the Rhymney and Taff valleys in the heart of the south Wales coalfield — from Llanishen Reservoir north of Cardiff and upland Rhymney Valley reservoir catchments, treated at Llanishen Water Treatment Works. At 61 mg/L (4.3°Clark) and a TDS of just 101.4 mg/L, Nelson's water is soft — consistent with the soft upland south Wales reservoir supply that characterises water quality throughout the Caerphilly county communities.

Nelson lies in the Caerphilly Basin coalfield where the Carboniferous Coal Measures and Millstone Grit valley geology produces acid, mineral-poor runoff water. Welsh Water draws on upland reservoir catchments in the Rhymney Valley and adjacent river systems, where the Carboniferous Grit and Shale uplands yield soft, calcium-poor water. The resulting 61 mg/L with TDS 101.4 mg/L is characteristic of the soft upland south Wales reservoir supply zone, softer than the slightly harder Bargoed (115 mg/L) distribution sub-zone further up the Rhymney Valley.

At 61 mg/L, Nelson's soft water is comfortable for domestic use with minimal limescale demands. Descaling the kettle every two to three months is typically adequate. The combi-boiler benefits from a standard scale inhibitor as a sensible precaution. Washing-up liquid lathers well with modest quantities of product. Taps and shower heads remain relatively scale-free with only occasional maintenance. In older properties, residents should briefly run the cold tap before drinking, as soft water can be mildly corrosive to lead or copper plumbing — standard Welsh Water guidance for the soft upland Rhymney Valley supply communities.