Several outbreaks of hemolysis in hemodialysis patients have occurred when chloramines in the public water supply have not been adequately removed by the dialysis unit's water purification system. Chloramines are not removed by reverse osmosis or deionization, and need to be either adsorbed by filtration through granular activated carbon (GAC) or neutralized by chemical reduction by ascorbic acid (vitamin C) added to the dialysate. Chloramine levels in the incoming water can fluctuate unpredictably, and failures of both systems have occurred when chloramines have exhausted their capacity. The medical and technical issues associated with both methods are explored in detail. Safety depends on critical care in the design of the system and rigorous testing more than once daily. Most dialysis units now depend on GAC filters, two of which should be placed in series so that chloramine breakthrough can be detected after the first one, before the second one fails. Comprehensive standards in force in California have not yet been applied universally.