2 images come to mind. One is when you see people drinking from water fountains and they put their mouths right over the spout so that that all the backflow washes right over the spout. And Two is when you see kids put their mouths directly on the water nozzle, and of course, you also have the backflow issue. Probably not a big deal as far as catching anything is concerned but its enough to make me stop using water fountains.