If I eat fruit instead or fatty foods, drink only water, etc, could I lose weight? I was wondering how much weight each day I would lose.

You would probably lose weight, but this is VERY unhealthy. When you eat less than the recommended daily calorie amount, your body goes into starvation mode, in which it thinks that it is staving. What happens during this time is your body will begin to store its fat and it will use your muscle tissue for energy before using your fat stores. Women on average use about 1100 calories a day just breathing and using normal body function, so anything less than this is depriving your body, I would aim for about 1200-1500 calories per day depending on your starting weight.

Good luck!!

CinziaMonreale is right. Not only is it incredibly dangerous, but it's also entirely counterproductive, since your body will go into starvation mode, hoarde everything, and then whatever weight you lose (which would be mostly muscle and water, not long-term fat loss) would come right back as soon as you go back to eating normally.