Stenotrophomonas maltophilia is an emerging nosocomial pathogen in patients rendered neutropenic following cytoreductive therapy for malignancy. The identification of sources and routes of transmission of this bacterium is of importance in the development of strategies to prevent nosocomial acquisition of S. maltophilia. A previous study had shown high rates of faecal carriage of S. maltophilia amongst patients with haematological malignancy and, as bottled water was consumed by many patients, we determined the prevalence of S. maltophilia in both carbonated and non-carbonated commercially available bottled water. Whereas carbonated water did not yield bacterial growth, 22 samples of non-carbonated products had total viable bacterial counts (at 22 degrees C) ranging between 0 and 4.9 x 10(4)/mL. Three samples yielded S. maltophilia and a further eight grew Pseudomonas species. Isolates of S. maltophilia of both clinical and environmental origin were able to survive, or grow, in non-carbonated mineral water over a range of pH and temperature values, including refrigeration temperatures. We therefore recommend that neutropenic patients should not consume non-carbonated bottled mineral water.