I don't think the zombies have gotten into the pumping water supply. Other than that haven't they (the Tower folks) been relying on tub water and bottled water? I don't think they've taken any water from the ocean or other water source that could potentially be infected. Also the zombies would have to be bleeding in the water in order to infect it and as Ra1th said there is a ton of water to dilute the blood.
Bookmarks