In condensation reactions, the atoms th make up a water from what?
The water derives from an hydroxyl group on one of the reactants, and (usually) a hydrogen from another reagent.
Now, typically, in a condensation reaction, we spit out water molecules, and typically we would add an acid,
Esterification, the coupling of an acid and a alcohol, is a typical condensation reaction:
As water is a stable molecule, these reactions are thermodynamically downhill. Because we can remove the water molecule, as a volatile azeotrope with benzne or toluene, the reaction can be driven to completion.