Save your vodka for drinking or for parts cleaning, it isn't that good a disinfectant. In a past life I inspected water treatment plants.
To get rid of the mold in water bottles, mix a bottle cap, (about 1/2 tsp.) of 5% sodium hypochlorite bleach (clorox, purox, store brand) in the bottle full of water and let set over night. Then rinse thouroughly. Try to use bleach that hasn't had extra scents such as lemon added.