I have a variety of kiddie pools, water buckets and I have a mist system with several nozzles I use during the heat. We also put the sprinkler on the lawn where they are when its hot. Although it gets hot here, with plenty of water and lots of shade, they do ok. I can't imagine keeping ducks without water to play in.
As for them drinking their wastes, it is what ducks do. Keep the water reasonably clean, but don't stress over it. Dump your kiddie pool on your landscaping and tell your landlord you are fertilizing his plants! Watered down duckie wastes work great on grass and bushes. Probably not directly on veggies though, not clean enough.