Energy is something that is not recycled but must be available.
In case of photosynthesis, specifically the energy of photons of light(sunlight) is something that is just transferred and never recycled.
Water is absolutely essential for photosynthesis because it acts as hydrogen and electron donor.
The granum of chloroplast contains photosynthetic pigments in groups called photosystems.There are mainly two photosystems: 1 and 2.Now these photosystems absorb light and convert this energy into glucose through electrons.When they absorb energy, they release high energy electrons and energy of these electrons is converted into glucose.
Once the photosystem loses electrons, it cannot absorb light energy .To replenish these electrons, water is photolysed, releasing electrons which are again ejected.Hence water is a crucial non recyclable component of photosynthesis