Can humans live without eating food, just by drinking water? How long can we survive just by drinking water everyday?
This would vary a LOT depending on the amount of stored fat, previous diet, the weather and even the water drunk. Weeks though there is a good chance that a loss of electrolytes can cause health problems. (that's why I mention the water you drink, because many bottled water brands and wells have a bit of salt in them.)
Its hard to say from anecdotal experience. There are claims of 3 weeks being easy, but a medical study would be unethical because of the risks posed to the subjects.
You can remember this easily as the rule of threes:
You can survive:
- 3 minutes without air. (death by asphyxiation)
- 3 hours without shelter (death by hypothermia, heatstroke).
- 3 days without water. (death by dehydration)
- 3 weeks without food. (death by starvation)
Going beyond those guidelines will generally do you permanent damage.
Further reading: http://www.wildernesscollege.com/basic-survival-skills.html
Actually, he went water only for about 75 days (read that elsewhere, can't remember) and then they supplemented his water only diet with electrolytes. He's done it under medical supervision and gained 7 KG in 5 years after the fast. So the weight does stay off (obviously, if you go and stay into a healthier diet).