To keep most small animals from drowning in a water tank when all they want to do is get a drink, just look around for an old flat board or a stick and place it in the water with one end on top of the edge of the water tank and the other end floating in the water. If you can find a little baling wire attach it a little more permanently. This will allow mice, squirrels, and even birds to crawl out and will keep the water cleaner for the next hiker to come along. Many ranchers do this already but it is amazing how many water tanks I have seen that are death traps for critters.
Shade