If you mean this...
Legionella is a type of bacterium found naturally in freshwater environments, like lakes and streams. It can become a health concern when it grows and spreads in human-made building water systems like
Showerheads and sink faucets
Cooling towers (structures that contain water and a fan as part of centralized air cooling systems for building or industrial processes)
Hot tubs that aren’t drained after each use
Decorative fountains and water features
Hot water tanks and heaters
Large plumbing systems
Then I am quite knowing of it..A family friend almost died from it..They linked it to a swamp cooler..
Do I need to treat my water with chlorine before I store it? A few prepper sites recommend that you treat your water with chlorine before you seal its storage container. But if you’re using tap water from your city to fill your water storage, it’s unnecessary. Tap water has already been treated with chlorine.
Flushing your system with city water that has been treated, works just fine..Just don't leave it in the tank forever without flushing and re-filling..