what is the chemical reaction of C8H10N4O2 (caffeine)+ H2O?

Answer 1

As any coffee drinker knows, caffeine is actually stable in water, even hot water.

If you want to know how it might possibly react with water under extreme conditions (hydrothermal, strong acid, strong alkali) you would need to look at the structural formula and think about the reactivity of the different functional groups.