Most of my rides are urban. Most of my urban rides intentionally skirt or go through at least three of our many urban parks. Most of those parks having working fountains. Never seen the homeless showering in those fountains, but wouldn't be surprised to find it happens. I'm one of the least sick persons I know at times going years in a row not taking sick a day. Likely more genetics, but I like to joke about it being my extremely lax attitude towards germs, it boosts my immunity. I am the polar opposite of a germ-aphobe.
Writing this got me to thinking about how many gangway spigots I drank water out of as a kid when we played outside 90% of the summer. It was pretty rare someone actually chased us off.