I also live in the Phoenix area. It may depend on how you are delivering the water. For example I use drip, and so the water goes first on the ground and then begins to soak into the soil and it is a while before it reaches the roots. So as a result it would have cooled and I have never had issues. Since you are using misters then the very hot water goes directly to the leaves. I think most people in Phoenix try to avoid the spray as it loses a lot to evaporation and is not a very efficient method anyway.
another thought - all of my feeder lines are black, but they are nearly all buried under ground so that they don't get the brunt of the direct sun. This would reduce the temperature of any residual left in the line but also protect the pipe from the high UV load which will deteriorate most plastic fairly quickly here in the desert.
Just a couple of thoughts.