Find a way to carry more water. Bigger bottles, seatpost-mounted bottle cages, bottles in jersey pockets.

I drink about 128oz a day if I don't do anything that makes me break a sweat. When I ride, I drink about 32oz/1L per hour. Find places to stop in and refill. Find houses with nice people inside that will let you refill. When it gets to about 105 around here, my water disappears 30 miles into the ride. I've gone so far as to make my routes more like figure 8s on really hot days, so I can stop home and refuel.