As long as the water is comfortably warm it's fine. If it's so hot that it would burn your skin, it would certainly burn your colon.
You may find that alternating warm and then cool enemas gives you even greater release. The colon reacts to changes in temperature either way, and some people expel more when the water is cooler. Again, it should be comfortably cool...you don't want to turn into a popsicle! ; )