I have a shallow feed tub with water in it for the barn cats; the chickens like to stand in it on hot days - and our summers are always hot and humid. Humidity does make a difference to hens in that when they ventilate (pant) they are benefiting from evaporation in their mouths and respiratory system. I keep a fan running in the coop area to keep fresh air circulating. I also have never lost a hen to overheating.
