water of hydration
n 1: the water present in hydrated compounds [syn: {water of
crystallization}, {water of crystallisation}, {water of
hydration}]
Hydration \Hy*dra"tion\, n. (Chem.)
The act of becoming, or state of being, a hydrate.
[1913 Webster]
{Water of hydration} (Chem.), water chemically combined with
some substance to form a hydrate; -- distinguished from
{water of crystallization}.
[1913 Webster]