Blackwood Water Hardness & Quality Report (2026)

Dŵr Cymru Welsh Water supplies Blackwood, the principal town of the Sirhowy Valley in Caerphilly County Borough in the South Wales Valleys, from upland reservoirs in the Sirhowy Valley and the wider South Wales Coalfield upland supply chain, treated at regional Caerphilly area works before distribution. At 116 mg/L (8.1°Clark), Blackwood's water is moderately soft, consistent with the upland Coalfield reservoir supply character that defines water quality throughout the South Wales Valleys.

The South Wales Coalfield uplands above Blackwood and the Sirhowy Valley are underlain by Millstone Grit (Lower Carboniferous sandstone and shale), Lower Coal Measures, and thin Carboniferous Limestone bands. The upland plateau drains acid peat moorland with low calcium release, but the scattered limestone outcrops and thin coal measure shales contribute a modest calcium increment to the reservoir supply. The resulting 116 mg/L supply with TDS 252.7 mg/L reflects the classic mixed-character South Wales Coalfield supply — softer than English lowland chalk areas but not as soft as the highest Welsh moorland catchments above 400 m elevation.

At 116 mg/L, Blackwood's moderately soft water is relatively comfortable for domestic use. Limescale accumulates at a gentle rate; descaling the kettle every six to eight weeks is typically adequate. The combi-boiler benefits from a standard scale inhibitor as a sensible precaution. Washing-up liquid lathers well at everyday quantities. Taps and shower heads develop only light deposits over several weeks; a monthly wipe with white vinegar keeps fixtures in good condition. The clean Valleys reservoir supply has long been prized in the South Wales industrial communities, and Blackwood's moderately soft water continues that tradition in the twenty-first century.