Answer: Water is considered as a reactant.
Step-by-step explanation:
In a chemical equation, the chemical species are termed as reactants or products.
Reactants are defined as the species which react in the reaction and are written on the left side of the reaction arrow.
Products are defined as the species which are produced in the reaction and are written on the right side of the reaction arrow.
Photosynthesis reaction is defined as the process in which green plants make their own food with the help of carbon dioxide and water in the presence of sunlight.
The chemical equation representing this reaction follows:

Here, the reactants are carbon dioxide and water. The products are glucose and oxygen molecule.
Hence, water is considered as a reactant.