We moved from Calif to Texas in March, got chicks mid May, 6 were Buff Orpingtons. This summer we had 70 days straight of over 100 deg temp, some days were 110. Their run is under a huge oak tree, I froze gallon water bottle, 4 - 5 a day for them to use.
I had two containers of water, both were oil drain pans, big enough to hold a gallon bottle of water, and enough room for them to drink from the sides. I also kept a water in their coop, with a frozen bottle in that also.
3 - 4 times a day I went out and misted them with the water hose, we were on water restriction, so I was not able to hook up a misting system for them. I also put a fan in their coop that ran all summer, with no excess cost to our electric bill. Hubby had our house at a cool 70 degrees, and our monthly bill was $250. Which according to our local electric company was good, said we must have good insulation.
There were a few days my girls were panting, but then so was I.
I also have 3 BR, 3 EE & 2 Light Brahma's & on GLW roo. They all made it through their first Texas Summer just fine. Am waiting to see what they think of snow when we get it. Rain don't bother them any more, they walk around like it was not even raining.