A person will probably die without water after 5 days, but will suffer serious, adverse effects after 3 days. There are a number of dependent factors that will determine how long it would take. First, the weather conditions; obviously if you are in a desert, water is evaporating away from your body quickly, so the time would be less; not to mention the sunstroke! If you are eating, food provides you with some water, but probably takes more water to digest than it provides. After 3-4 days without water, if you are not already dead, if you manage to find some water, the damage done to your internal organs may be permanent.
All of the figures that I have read say 10 to 20 days without food. Obviously, this depends upon your weight to begin with and your state of health before the eating stopped. An overweight adult will last longer because they have more reserves to work from than a thin person. Ghandi went 21 days without food and survived. He didn’t have very much body fat to work with. Terry Schiavo made it almost 2 weeks. One source that I read said that as long as a person has water, they can survive up to 8 weeks without food. I am skeptical.