The main component of the cells in the human body is water, constituting about 60-70% of cell mass. Water is vital for various cellular processes, serving as a solvent, medium for biochemical reactions, and a temperature regulator. It also transports nutrients, hormones, and waste products within and between cells. Water's unique properties, such as cohesion, adhesion, and high heat capacity, make it essential for maintaining cellular functions and overall homeostasis in the human body.