Seconding this. Back in the 50's and 60's, the top Tour de France contenders would tell people not to eat or drink anything before or during a race, for fear t

Seconding this. Back in the 50's and 60's, the top Tour de France contenders would tell people not to eat or drink anything before or during a race, for fear that their stomach would start digestion and rob them of power. Several of them died on the tour essentially of exertion and dehydration. Your body will not tell you when you are dehydrated until it is too late. Your mind can get clouded, you can get delusional, and then lost. You might try to wander around and an accident will happen. Or you might get really tired and decide to sit down and wait for someone to come by you. It's just stupid to go out for multi-hour hikes or runs in the wilderness without the essentials (such as water).