During a hotel shutdown of three floors for six months, what is the most effective measure for Legionella control?

Draining the piping serving the shut floors is the most effective measure for Legionella control during a prolonged shutdown like this. When water sits stagnant in pipes for an extended period, there is a significant risk for Legionella bacteria to proliferate. By draining the piping, the potential for bacterial growth is eliminated, as Legionella requires water to survive and reproduce.

With a hotel shutdown spanning six months, simply relocating guests to other floors does not address the risk posed by stagnant water in the unused plumbing systems. Running all faucets daily can help mitigate some of the risks associated with stagnation by refreshing the water in active systems, but it does not impact the shut-off systems. Using bottled water also does not effectively mitigate the risk of Legionella in the plumbing systems since it does not address the water that remains in the pipes serving those floors.

Therefore, draining the piping is the most direct and effective way to prevent the risks associated with Legionella growth during the extended downtime of those floors.