The research through the survey included data collection on the technical and technological characteristics from three hotels and one home for the elderly and disabled located in the Split – Dalmatia County. The survey included data on water supply source, type of construction material for the distribution and internal networks, heating system and water heater type, working hours of each facility, and water consumption. In the period from 2009 to 2012, 425 hot water samples from all four facilities have been analysed. Physical and chemical parameters (temperature, pH, free chlorine residual concentrations, Fe, Zn, Cu, Mn, Ca and Mg) were determined in the samples, as well as the presence and concentration of bacteria Legionella spp.. The Spearman correlation coefficient determined the correlations between the physical and chemical parameters and technical and technological characteristics of heating systems and the presence of Legionella spp.. The temperature is an important factor for the development of biofilms and it is in negative correlation with the appearance of Legionella spp.. Above the median value of 53.10°C, Legionella spp. has been determined in only two samples, which means that higher temperatures negatively affect the colonisation of Legionella spp.. It was proven that the free chlorine residual is not an efficient disinfectant, because Legionella spp. has been identified in samples with and without the free chlorine residual. Metal ions present in water occur as products of corrosion. Positive correlations between the Fe and Zn concentrations and Legionella spp. were established, while the inhibitory effect of a higher Cu concentration on Legionella spp. concentration was proven. Legionella spp. was identified in 30.2% of the water samples from the heating system with galvanised pipes, as well as in 26.1% of the samples from systems with plastic pipes. This difference is not significant, which is explained by the positive effect of organic additives that enter water from the structure of plastic pipes and rubber seals on the development of Legionella spp.. Systems with plastic pipes also have various metal parts, which are subject of corrosion and contribute to an increased concentration of metal ions in the water. Approximately the same number of samples positive to Legionella spp. was established regardless on the type of the hot water preparation system.