Hydrolysis which is key in the digestive process, requires water. In this process, water is inserted into a nutrient and enzymes are present to catalyze the reaction. The nutrient is broken down to its smallest subunit. For instance, hydrolysis of starch results in the formation of glucose, a smaller molecule that can be used by cells in cellular respiration. Likewise, water is produced as a waste product of cellular respiration and is needed as a raw material in the photosynthesis reaction. Water makes up most of the volume of the cell and is needed to prevent dehydration. It is the universal solvent and many chemicals dissolve in water. It is the main component of blood plasma.
The presence of water is crucial in photosynthesis and in cellular respiration. These are biochemical reactions which could not be happening without water.
Water helps in body temperature regulation, ensuring the normal functioning of organisms.
The transport of substances from cells to tissues is done by the water.
The existence of enzymatic activity wouldn't be possible without water.