I have a kiddie pool that I dump and rinse out daily... usually they have the pond, but sometimes I need them contained, then it's just the pool in their pen.. anyway, my SIL came over at around 10am one day (i changed the water at like 7am), and was all horrified by the water gunk... she was so cute, and said 'uh, would it help if I changed the water for the ducks?', all nice and helpful, but in a totally grossed out, didn't want to be rude, kind of way... i explained that I had just changed it, (she didn't believe me) and we changed it again... within 1/2 an hour, the water was back to the way it had been, half full of dirt, mud and poo... and she was SO SHOCKED!!! and apologetic.