Patients undergoing hemodialysis are at an increased risk for bloodstream infections (BSIs). Infection usually occurs because of contamination of water supply, water treatment, distribution systems, or reprocessing dialyzers. Here, we report an outbreak of BSIs caused by Stenotrophomonas maltophilia (n = 21) and Burkholderia cepacia (n = 22) among dialyzed patients at a large hemodialysis center in Brazil. Overall, three patients died (7%), two of which had bacteremia caused by S. maltophilia and the other had a B. cepacia infection. We collected water samples from different points of the hemodialysis system for culture and typing. Genetic patterns were identified through polymerase chain reaction-random amplified polymorphic DNA (PCR-RAPD) and pulsed-field gel electrophoresis. The same genotypes of S. maltophilia and B. cepacia recovered from blood cultures were found in dialysis water. Also, multiple genetic profiles were identified among water isolates, suggesting heavy contamination. Bacteremia cases persisted even after implementing standard control measures, which led us to believe that the piping system was contaminated with microbial biofilms. Soon after we changed the entire plumbing system, reported cases dropped back to the number typically expected, and the outbreak came to an end.