I'm lucky I have a creek in my parents backyard, that has finally been cleared as "clean". For years it would get tremendous amounts of farm runoff/pesticides making it highly toxic.
As a kid I used to catch crawdads out of it and release them back, then when I was about 15 they said don't play around it and all the wildlife, minnows, snakes, toads, frogs and such, disappeared. In the past few years the creek has been coming back strong, which means the return of snakes (I know how survival loooooooooooves snakes). The anacharis is starting to come back in large quantities which is where the crawdads would hide, I feel like if there was a SHTF most of the students would leave trying to get home to mommy and daddy and this creek would go unnoticed by most.
Also, bird baths and water features in nicer neighborhoods (koi ponds, fountains)
I do not know if it has been said, but like the guy on doomsday preppers did with the moss sponge. Also, digging a hole in the ground, putting a cut in the middle, putting a plastic garbage bag over it and a small pen hole for the water to go through into the cup. Also putting a small rock in the middle so that it will make a funnel.