Water is a major component of cells. It has several properties that are important in biology. In particular, water:

- is a metabolite in many metabolic reactions, including condensation and hydrolysis reactions
- is an important solvent in which metabolic reactions occur
- has a relatively high heat capacity, buffering changes in temperature
- has a relatively large latent heat of vaporisation, providing a cooling effect with little loss of water through evaporation
- has strong cohesion between water molecules; this supports columns of water in the tube-like transport cells of plants and produces surface tension where water meets air.