Also, consider getting insulated water bottles.
Polar makes them; others might as well. They work well to avoid the "boiling cauldron of undrinkable liquid" syndrome (at least for a while...).
My ride home was unpleasantly hot today as well; I had two polar bottles (30 mile ride) that I had filled with tap water just before leaving, and they were still plenty drinkable when I got home two hours later.