It has been very hot where I am with temps in the mid to upper 90's with heat indexes of 105.
I too do the ice in their water but what I have found works the best is the garden hose.
I simply use the shower setting and well get them wet. I must admit they don't like it much but the heavy panting and wings held out from the body stops. Since I started doing this several years ago I have only lost one bird to heat and she was approaching 8 years of age.
My personal experience, (showing my age I have over 35 years) is that the night time tempature affects egg production and survivability.
If the nightime temp stays 80 or higher it is extremely tough on chickens. They simply do not cool down at any point during a 24 hour period.
The one thing with the garden hose is they will run from you so this can stress them. I simply move slowly while I am in the run, I only turn the faucet on about 25% pressure and avoid as much as possible in getting their heads wet.
Hope this helps