Thanks everyone, My boys live in cages in a stone shed with a plastic roof. The door is in two halfs so the bottom is shut and the top is open, and it has a detachable screen to keep cats etc out but the fresh air in. But it does get hot so the bottles are a good idea to keep them cool in the hot weather. (in the cold weather they come inside to the spare bedroom )
When the sun goes over abit I put them in the garden in two seperate runs and large garden umbrella's are put up to give extra shade. They were out today for about 4 hours on the grass.