Hard water syndrome: a case series of 30 patients from a London haemodialysis unit

Severe and life-threatening hypercalcaemia can develop in haemodialysis patients dialysed against a dialysate with a high calcium concentration, the so-called hard water syndrome. Here we describe the development of hard water syndrome in 30 patients following sequential failure of the reverse osmosis unit and water softeners. Serum calcium levels rose from 2.43 ± 0.19 to 3.92 ± 0.51 mmol/L after exposure. All patients required emergency haemodialysis and four acutely deteriorated, one of whom was 24 weeks pregnant. This is the largest reported series of patients affected by this rare and severe condition. This event led to the introduction of processes to minimize future risks.