Bonnyrigg Water Hardness & Quality Report (2026)

Scottish Water supplies Bonnyrigg in Midlothian, a residential town south of Edinburgh, from Glencorse Reservoir and Loganlea Reservoir impounded in the Pentland Hills south-west of Edinburgh, treated at Glencorse Water Treatment Works before distribution across Midlothian and parts of Edinburgh's southern supply zone. At 30 mg/L (2.1°Clark), Bonnyrigg's water is very soft — one of the softest in the dataset — driven by the ancient Pentland Hills greywacke and volcanic rock geology that is essentially inert to calcium carbonate dissolution.

The Pentland Hills reservoir catchments drain Lower Palaeozoic greywackes, mudstones, and Devonian volcanic rocks — hard, chemically resistant formations with virtually no soluble calcium. Rainfall on the Pentland uplands passes over thin peaty soils and through these ancient rocks without acquiring significant mineral content. Glencorse Reservoir and Loganlea Reservoir receive this chemically inert, very soft water, and with a TDS of just 54.5 mg/L, the dissolved mineral content is exceptionally low — barely above rain water — making Bonnyrigg's supply among the purest in lowland Scotland.

At 30 mg/L, limescale is virtually absent in Bonnyrigg homes. Descaling the kettle once or twice a year is all that is generally needed. The combi-boiler requires no scale inhibitor for calcium protection, though soft water can be mildly corrosive to metal surfaces over time; a corrosion inhibitor in the central heating circuit is still recommended. Washing-up liquid produces excellent lather with minimal product. Taps and shower heads remain clean almost indefinitely. Residents with older lead pipework should briefly run taps before drinking, as very soft water dissolves lead more readily than hard water.