Root Temperature

[hald]

I'm using containers with water reservoirs. I'd like to rig up some automatic watering system because I'm watering about 4 times a day. The containers\plants are in afternoon shade. The "problem" is our hot climate.

Are tomato roots affected much by temperature? Is cool water 4 times a day beneficial? Conversely, if I maintained a constant water level in the reservoirs would the warm water be detrimental. Or does it matter much at all?
-Hal