The document discusses Legionella risks associated with hot water systems. It notes that hot water cylinders are a major source of Legionella bacteria, which can spread through fine water mists. Guidelines recommend storing hot water at 60°C and distributing it at 50°C to avoid bacterial growth, but scalding regulations require lower temperatures in places like nurseries. Installing thermostatic mixer valves (TMVs) can blend hot water down to a safe temperature at outlets, but retrofitting buildings with TMVs is expensive. Some opt to store water at 40°C instead, allowing bacterial growth. TMVs also require proper installation close to outlets to prevent colonization in pipe runs.