The term that describes a chemical reaction in which water is gained is called dehydration synthesis.
Water plays a fundamental role for life, as well as in the reactions that break down biological molecules in order torelease subunits that the body can use. When complex biological molecules in the body are synthesized, water is usually generated as a byproduct.
The subunits that form the large biological molecules are joined by a chemical reaction called synthesis by dehydration, which consists in the elimination of a hydrogen ion from a subunit and the elimination of a hydroxyl ion of a second subunit, to create gaps in the outer electron layers in the atoms of both subunits. These gaps are completed by sharing electrons between the subunits, to generate a covalent bond that can bring them together. Then, the hydrogen and hydroxyl ions combine to form a water molecule.