Water treatment is a vital aspect of hemodialysis in which knowledge and technical skills are of utmost importance. The recognition that nontuberculous mycobacteria can be resistant to certain germicides spurred the establishment of the current safety microbiologic standards for dialyzer reprocessing. Monitoring the dialyzer membrane integrity is as important as meeting the standards for bacterial and endotoxin levels for dialyzer reprocessing. Ensuring the use of product water that meets the chemical and microbiologic standards of the Association for the Advancement of Medical Instrumentation is necessary to reduce the incidence of endotoxemia and chemical hazards associated with the use of water for hemodialysis. The pathogenesis of febrile reactions during hemodialysis remains controversial. The weight of evidence, however, favors transmission of endotoxin fragments across dialysis membranes to induce mononuclear cell cytokine production.