Hardness water level of major cities in the UK Area Primary source Level[42] Manchester Lake District (Haweswater, Thirlmere) Pennines (Longdendale Chain) 1.750 °clark / 25 ppm[43] Birmingham Elan Valley Reservoirs 3 °clark / 42.8 ppm[44] Bristol Mendip Hills (Bristol Reservoirs) 16 °clark / 228.5 ppm[45] Southampton Bewl Water 18.76 °clark / 268 ppm[46] London (EC1A) Lee Valley Reservoir Chain 19.3 °clark / 275 ppm[47]