Background: Carbapenemase-producing Enterobacterales (CPE) have rapidly emerged in Europe, being responsible for nosocomial outbreaks. Aim: Following an outbreak in the burn unit of Ghent University Hospital, we investigated whether CPE can spread between toilets through drain water and therefrom be transmitted to patients. Methods: In 2017, the burn centre of our hospital experienced an outbreak of OXA-48-producing Klebsiella pneumoniae that affected five patients staying in three different rooms. Environmental samples were collected from the sink, shower, shower stretcher, hand rail of the bed, nursing carts, toilets, and drain water to explore a common source. Whole-genome sequencing and phylogenetic analysis was performed on K. pneumoniae outbreak isolates and two random K. pneumoniae isolates. Findings: OXA-48-producing K. pneumoniae was detected in toilet water in four out of six rooms and drain water between two rooms. The strain persisted in two out of six rooms after two months of daily disinfection with bleach. All outbreak isolates belonged to sequence type (ST) 15 and showed isogenicity (<15 allele differences). This suggests that the strain may have spread between rooms by drain water. Unexpectedly, one random isolate obtained from a patient who became colonized while residing at the geriatric ward clustered with the outbreak isolates, suggesting the outbreak to be larger than expected. Daily application of bleach tended to be superior to acetic acid to disinfect toilet water; however, disinfection did not completely prevent the presence of carbapenemase-producing K. pneumoniae in toilet water. Conclusion: Toilet drain water may be a potential source of hospital room-to-room transmission of carbapenemase-producing K. pneumoniae.