I've read that giving hens frozen watermelon helps keep them cool but they have no interest in it, could I put it in their waterer to see if they get use to the taste?
If they don't like the frozen watermelon I wouldn't put it in their water. If they don't like it they may not drink their water of it tastes like something they dislike. Try other frozen melons or fruits. Strawberries are something my chickens love, try those.