I was having trouble following how far you rode and how much you drank, but I got the impression you were drinking far less than I would. Riding in heat and humidity takes some acclimation and some of us adjust to it better than others. Drink plenty before you ride and drink at least a bottle per hour while you ride. Make sure to add in some electrolytes via drinks, gels or supplements if you are riding more than a couple of hours. Most people can adjust to riding in heat if they ease into it and take in what the body needs.