I am from Australia. I live in North west Queensland. Incidentally yes, heat can kill your chooks, particularly silkies. I used to have a sprinkler system set up on the roof of the shed to come on for about 10 minutes each hour in summer just to cook the top down when I was at work. You also need to make sure that your water is in places that will stay cooler. Boiling water is no different to no water at all.
Hope you answer, us Australians are getting a bit lonely here so could stick together.