You can survive much longer without food than you can without water. Humans have been known to survive up to 8 weeks without food IF they have water. Survival without water may be 3-7 days (100 hours at an average temperature outdoors). Normally there’s more water inside cells than outside; dehydration reverses that ratio. The duration of survival depends on body weight, genetic variation, level of health, and the presence or absence of dehydration. In presence of dehydration, the stress response is triggered and brain areas related to anger, fear, and alertness are activated. You lose water every time you exhale, when you sweat, when you discharge urine and feces, and if you vomit or throw up. This water must be replaced. More tomorrow.