Portishead Water Hardness & Quality Report (2026)

Portishead, the North Somerset coastal town on the Bristol Channel south-west of Bristol at the mouth of the Gordano valley, is supplied by Bristol Water. Supply to North Somerset and the Bristol-Portishead corridor draws on the Barrow Gurney and Blagdon Reservoirs in the north Somerset lowlands south of Bristol, supplemented by the Cheddar Reservoir (fed from the Mendip catchment) and groundwater from the Carboniferous Limestone Aquifer of the Mendip Hills. Bristol Water treats the blend at Barrow Water Treatment Works before distribution north-west to Portishead and the North Somerset coast. The Mendip catchment drains Carboniferous limestone — the same porous carboniferous geology that forms the famous Cheddar Gorge — yielding moderately hard spring and groundwater. The TDS of 407 mg/L reflects a mixed surface-water and limestone groundwater supply with moderate calcium bicarbonate content.

The Carboniferous Limestone (Dinantian) of the Mendip Hills is the primary hardness-contributing geology in the Bristol Water supply zone. Rainwater percolating through the limestone karst dissolves calcium carbonate from the porous carboniferous rock, yielding spring and groundwater at 150–180 mg/L. Surface water from the Blagdon and Barrow Gurney reservoirs adds softer runoff from the Triassic Keuper Marl and Lias lowlands, moderating the overall hardness. The blend produces the characteristic 155–165 mg/L range typical of the northern Mendip fringe supply for the North Somerset and Bristol area.

At 162 mg/L Portishead's water is moderately hard and limescale is a manageable household concern. Kettles benefit from descaling every five to six weeks with a citric acid tablet or white vinegar soak. Shower screens develop moderate calcium spotting that responds to regular treatment with diluted white vinegar spray. Washing-up liquid lathers adequately. Combi-boilers and white goods face moderate scaling risk. Portishead's transformation from industrial dockyard town to sought-after commuter destination on the Bristol Channel has not changed its moderately hard Mendip-limestone-influenced water supply, which typifies the Bristol and North Somerset region.