Multi-resistant Pseudomonas aeruginosa (MRPa) has been isolated from patients in a Western Australian teaching hospital with increasing frequency since first encountered in 2006. Between 2006 and 2008 the number of patients with MRPa increased from three to nine per annum, and their location shifted from intensive care to a high dependency unit. A novel water-saving device (aerator) in a staff hand basin was identified as a likely disseminator, with MRPa being isolated from biofilm in the basin's plumbing. The disposal of patient waste, surplus intravenous antibiotic infusions and solid items via hand basins were possible contributory factors. Genotyping of MRPa from patients in other hospitals showed distinct genotypic lineages. The third seasonal cluster persisted for longer, indicating adaption to environment. More effective environmental control of P. aeruginosa is urgently needed.