My mother forbade me from using public water fountains. But then, she was a microbiology major and also forbade me from going outside barefoot. And yes, in school I saw some kids put their mouths on the fixture. EEW. If need be, I'll use them, but I'll run the water for a couple seconds. I mainly use outdoor ones for refilling water bottles. Indoor ones...if the water's cold and doesn't taste nasty, sure. I don't have that kind of luck, at least in the last few buildings I've worked in.