A study was carried out over a 4-month winter period in order to assess the presence of filamentous fungi in the water distribution system of the University Hospital of Liège. A total of 197 hot and cold water samples were collected from the main water supply lines and from the taps at three different hospital sites. Overall, filamentous fungi were recovered from 55% and 50% of the main water distribution system and tap water samples, respectively, with a mean of 3.5 ± 1.5 colony forming units per 500 ml water. Nine different genera were identified, all belonging to the Hyphomycetes class. Aspergillus spp. were recovered from 6% of the samples of the water distribution system and A. fumigatus was the most frequently recovered species (66.6%). However, this species was not isolated from water taps. Fusarium spp. was predominant at one site, where it was found in 28% of tap water samples. No Aspergillus spp. but some Fusarium spp. isolates were identified in samples collected from high-risk units. Filters were introduced at the point-of-use in the haematology unit after completion of the study. The findings of the present study confirm the need for further documented studies to evaluate the safety of the hospital water system and to define new preventive measures.