I have been contemplating putting used gutters on one of the coops to catch rain water etc. And I hear you about the clean water dish! I end up gathering them all up and putting them in the kiddie pool with a bit of bleach. Unfun!
We will be puting a gutter on the back of our coop for two reasons. 1. We designed the coop with a slight pitch (6' in the back, 7' in the front) so we will need to keep the the rain from washing the foundation away in the back. And 2. I want to eventually install a rain barrel to offset the cost of water. Although my DH doesn't see the point in it lol