In recent years, hospital infections caused by opportunist microorganisms in immunsupressed patient group are becoming gradually important. It is determined that these microorganisms grow easily in water distribution systems even producing biofilm from time to time. In this research, it was aimed to determine microbial population in water samples taken from distribution system of a grand hospital. For this purpose water samples collected from 100 different points of water distribution system belonging to different units of the hospital were analyzed in terms of bacteriology and mycology. In these analysis, membrane filter method was used. Samples were examined with bacteriological and mycological methods. In 84 (84%) samples most frequent bacteria determined were Bacillus spp (77%), Bacillus cereus (11%) and Pseudomonas (5%), staphyllococci (4%) and the rest were miscellaneous bacteria and in 16 samples (16%) more than one type of bacteria were isolated. In 51 samples (51%), 16 types of mold were isolated, Penicillium spp (24%), Aspergillus (8%) Acromonium spp (5%) were more frequent and in 13 samples (13%) it was determined that more than one type of fungi reproduced. In six samples no growth of fungi was observed.

Finally, Spearman correlation test was applied to determine the correlation between the growths of isolated bacteria and fungi, but correlation was not found.