The average healthy person can survive 40 days without food, as long as they drink plenty of water, and keep a low activity level. A married couple I've heard of did this - went 40 days with only water - they physically hurt themselves, but they're still alive today. They've done at least one other 40 day fast, but they made sure to get nourishment from juice and broth.
The gospels only say that Jesus did not eat anything. There are no comments about drinking water. It appears that Jesus did drink water. Medical literature says a man or woman cannot live long without water, but we can live a long time without food.