The first important point about keeping chickens comfortable in hot conditions is to get a breed that can tolerate the conditions they are likely to be subjected to.
What is apparent here (It was 106 Fahrenheit midday today) is shade is vital. However there is shade and shade. A single layer placed a few feet above a run, or shelter can easily trap the rising hot air (See picture on home page for this thread). Trees for example let hot air rise through the branches and also prevent the lower foliage from getting heated.
The ideal type of shade seems to be either tall bushes/cane or dense undergrowth beneath trees.
Something like these options.
During the heat of the day Tribe 1 stay down the bank on the left of the picture.
A large tall bush. This cane and a favorite area of safety and shade for Tribe 3.
Plenty of air movement and shade under this large bush.
In the pictures above the temperatures were 90 degrees +.
A chickens core body temperature is around 106 degrees Fahrenheit. As soon as the ambient temperature reaches this a chicken can no longer transfer body heat to it's environment. It doesn't make a lot of difference what cold things you give it to eat, they won't alter the chickens temperature although they will provide some hydration in the case of say watermelon. We humans drink water or cold drinks because our heat regulation is done through sweating but chickens don't have sweat glands so this doesn't work for them.
Misting with water may seem like a good idea but a mist won't penetrate they chickens feathers and their skin temperature is likely to remain the same.
One of the less noticeable ways a chicken has of regulating it's temperature is through feather adjustment. The same mechanism they use (Filoplumes) to raise and lower their feathers to protect them from the cold also works to improve airflow close to the skin. The holding out of the wings assists the airflow increased by raising the feather with the Filoplumes, giving a greater surface area exposed to any air movement.
Part of the problem for chickens in the heat is they don't sweat and they are reliant on losing body heat primarily through their combs, wattles and mouth.
For chickens confined in a run a space under the coop if available makes good shade. The sun heat doesn't penetrate to the floor and heat is still able to rise into the coop.
Best of all is shade provided by foliage. Very hard to better what nature provides.
One method used where I live to provide shade for chickens in runs is to cut small tree branches and lay them on the roof of the run. Even is your run couldn't support branches you could still make a makeshift frame, cover the with branches and place it in the run.
Another alternative is to buy wall insulation slabs, the thicker the better and construct a three sided box with the reflective foil on the outside. An arrangement such as this might work well in the urban environment.
The main points I wanted to stress are chickens don't sweat so trying to pour water down them isn't going to work, and well thought out shade that doesn't restrict any breeze is the best solution.
