Hemodialysis-associated febrile episodes: surveillance before and after major alteration in the water treatment system. Surveillance for bacteremic or pyrogenic episodes associated with hemodialysis was undertaken before and after the reconstruction of the water treatment system at our University medical center. The new water system included a holding tank with iodination treatment. The water delivered to individual dialysis stations had only occasional positive bacterial cultures (3 of 21 samples before completion of construction, 2 of 16 samples afterwards) and intermittent detection of endotoxin (6 of 21 samples before completion of construction, 9 of 16 samples afterwards) at monthly sampling. Among 51 individual dialysis treatments (25 patients) before reconstruction and 56 treatments (29 patients), after, only 2 and 3 febrile events were identified, respectively. All of these were associated with underlying infectious illness and not with the hemodialysis procedure itself. Overall, we conclude that pyrogenic episodes associated directly with hemodialysis treatment are infrequent, and that the addition of a water storage tank with iodination treatment does not appear to increase the risk of bacteremia or pyrogenic episodes. 