guess it wont work like I had planned, good thing we got a good discussion here rather than me trying and seeing the hazards spread in real life.
But I know I will have a pond / fountain for them, with excellent filtration to kill germs so the water will always be good for drinking and bathing

an acquaintance of mine kept local finches (javas, munias, strawberries, etc), and their drinking water is a used aquarium with lots of aquatic plants and a few small fish to eat mosquito larvae!
and the finches are doing just fine! he even said some of them are bold enough to go for a splash, and came back to dry themselves up