My brush with heat problems came my first summer commuting. While that 8 mile commute seems like nothing now, it was work back then. With temps in the teens (110-115), I would 'pre-hydrate' for the ride home, and then rely on my Camelbak. But I was really busy one afternoon, had not pre-hydrated, and had not refilled my pack. I ran out of water, not far from from home, but by the time I got there I was no longer sweating, was feeling disoriented, and like I was going to collapse. I grabbed water and jumped in the shower until I felt I was recovering. Good thing it wasn't longer. In our dry climate, you can manage the heat IF you hydrate. Otherwise... you become a statistic.
Our group rides here start as early as 5:30 in the summer. The night before, I freeze a bottle of Sustained Energy, and about two-thirds of a water bottle, which I top off with cold water on the way out. That gets me 1.5-2 hours before a stop to refill, and the water is still a 'tolerable temp'. Even starting frozen, what's left of the SE gets rancid by then, and I replace it with ice-water at the stop, giving me two bottles for the rest of the ride. I find that my drinking increases steadily during the course of a summar ride, even though the last part is often less strenuous. So, even if there is not much distance left, if I am running out, I remind myself NOT to conserve, and stop somewhere to refill.