Where I live, I can drink over 200oz of water on a long hot summer ride, and still lose 2-3% of my body weight. Waiting to drink until 'thirsty' could be life threatening. With that much water flowing through, you obviously have to also be popping electrolytes, and I take enough to ensure my sweat is salty. Learning to manage hydration (and nutrition) is a huge part of the endurance learning curve, and oversimplifying it is dangerous.