The average bather puts in fifty milliliters of urine and about a liter of sweat per hour in active swimming. The chlorine goes so fast with all the kids whizzing in there. We've found potentially disease-causing viruses in every public wading pool we've tested. Microbes in space vehicles pose unique challenges. If we're going to go to Mars, we have to think about this kind of thing.
Russian astronauts have a few other things to think about first.
One thing you don't want is for your space station to degrade. Microbially, the best public restrooms are in hospitals. If you want the cleanest, pull in to the emergency room. Next are your fast-food restaurants, and the worst are airports and bus stations. The more stalls the better, by the way.