Drinking a large amount of water during hot weather can cause watery droppings in chickens. If you have a regular vet, collect a few fresh droppings, and you can get a fecal float to look for worms and coccidiosis, both of which can cause runny droppings. Two to three times a week, you can offer a bit of plain probiotic yogurt mixed into their feed in a large wide bowl for gut health. I usually add water to spread it around in the feed .