Microbiological and Physicochemical Parameters Related to Legionella spp. Colonisation in Hot Water Distribution Systems in Madrid: Case Study in Sports Centres

Domestic hot water systems are one of the most important reservoirs of Legionella. It is thought that physicochemical and microbiological water quality influences bacterial development. Accordingly, the objective of this study was to evaluate this relationship in domestic hot water in public buildings in Madrid for potential health risks and to assess the parameters that could be associated with Legionella contamination, which would assist in developing control strategies to prevent legionellosis. A total of 1695 DHW samples were evaluated over a 14-year period (2007–2020). Legionella was analysed using culture plates and qPCR. The influencing parameters (pH, electrical conductivity, colour, turbidity, Fe nitrites, and coliforms) were analysed following official methods. Furthermore, sport centre risk assessment was carried out. Legionella was isolated in 64 samples. Non-compliance levels for turbidity, colour, iron, nitrites and coliforms were found primarily in samples containing Legionella. Nitrites > 0.5 mg/L, turbidity > 1 NFU, colour ≥ 1 Pt/Co, and building type were good parameters to test Legionella colonisation. The selected influencing factors may be a useful tool for ensuring water supply quality.