What is the function of water in photosynthesis?
It doesn't necessarily have a function, but is a molecule that reacts with carbon dioxide to produce glucose.
Water is one of the reactants in photosynthesis, it provides the hydrogen needed to form glucose (a hydrocarbon).
Water and carbon dioxide enter the leaf through the stomata (small holes on the underside of the leaf that are controlled by gaurd cells) by diffusion.
The water is split during the light reaction to form oxygen gas and hydrogen ions. The hydrogen ions are used by the chloroplast to produce ATP.