Literature data on Legionella spp. presence in houses water networks have been increasing during the last years, but epidemiological reports assert a high incidence of Legionnaires’ disease infection in Italy. Updating our previously published data, we report a five-year survey on Legionella spp. colonization in 235 buildings with an independent hot water production (IB); 82 buildings with a central hot water production (CB); and 58 buildings with a solar thermal system for hot water production (TB). In all the 375 buildings Legionella spp. was researched in hot and cold water samples and microbiological potability standards of cold water were evaluated. Legionella spp. was detected in 27% of the water networks, mostly in CB and TB. We detected correlations between the presence of bacteria and some physical-chemical parameters (low chlorine level and optimal temperature for Legionella spp. growth). Cold water resulted free from microbiological hazards, except for coliform bacteria isolated in three separate cases, and Legionella spp., detected when cold water temperature was about 20°C. After a five-year survey we confirm the presence of a Legionnaires’ disease risk and the need of training programs for all the workers involved in residential water systems management.