For something so simple and tasteless, its importance to us cannot be overstated. It is the essence of life. War have been fought over water, but let's not get sidetracked.
Water makes up more than 2/3 of our body weight and facilitates so many of our body’s functions. Your chance of survival (without shelter) in extreme weather (hot or cold) is about 3 hrs. Staying longer than 3 days without water is fatal.