I'm in Texas as well and have a little kiddie pool in the coop with a little (like a half and inch) of water in it and I don't think they use it yet. I have found that if I spray down the coop a couple times a day they really like it. I also spray the grass they walk through a lot. Despite the heat and panting they still chase grass hoppers like crazy!
Another thing I've done it but a box fan out in the coop and put out some frozen water bottles. They love the fan and like to peck the frost off the bottles but they haven't really figured those out yet either.