Plymstock Water Hardness & Quality Report (2026)

Plymstock, the south Plymouth suburb in the City of Plymouth east of the Plym estuary on the fringe of the South Hams, is supplied by South West Water from a blend of Dartmoor upland reservoir water and local Plymouth limestone groundwater. Burrator Reservoir on the south-west flank of Dartmoor — draining the Dartmoor Granite moorland — is South West Water's primary Plymouth supply source, producing inherently very soft water (40–70 mg/L) from the hard, calcium-depleted Devonian granite. However, Plymstock's supply zone incorporates a significant proportion of groundwater from the Devonian Plymouth Limestone — the same Carboniferous and Devonian limestone that forms the dramatic gorge at the Plym estuary at Plymbridge and the Shaugh Bridge area. This limestone groundwater contributes substantially harder water (250–300 mg/L) to the distribution blend, elevating Plymstock's supply to 177.5 mg/L. The TDS of 454.4 mg/L confirms the limestone-groundwater mineral contribution in this south Plymouth supply zone.

The Devonian and Carboniferous Limestone of the south Plymouth area — the same limestone that forms the Plymouth Sound cliffs, Dunstone Point and the Cattedown Limestone worked for cement — dissolves calcium bicarbonate into groundwater infiltrating the karst limestone. South West Water blends this harder Plymouth limestone groundwater with the soft Dartmoor Burrator supply to produce the characteristic moderately hard 177.5 mg/L in Plymstock's distribution zone — noticeably harder than the soft Dartmoor-only supply zones of west Plymouth and Tavistock.

At 177.5 mg/L Plymstock's water is moderately hard and limescale management is a regular household task. Kettles benefit from descaling every four to six weeks with a citric acid tablet. Shower screens develop moderate calcium spotting that responds to regular white vinegar cleaning. Washing-up liquid lathers adequately. Combi-boilers benefit from inline scale inhibitor protection. Plymstock's residential suburban character in the rolling South Hams fringe east of Plymouth Sound combines Dartmoor moorland and Devonian limestone geology — a blend reflected directly in the moderately hard water from the tap.