What causes water's low vapor pressure?
The vapour pressure of water is depressed by the degree of intermolecular interaction (intermolecular force) present in liquid water.
There is a great deal of intermolecular interaction present in liquid water. This interaction arises from hydrogen bonding, in which electronegative oxygen atom polarizes electron density from the
The end result is a liquid with fairly strong intermolecular interaction (NOTE that intermolecular interaction is distinct from intramolecular interaction!). The vapour pressure of water is REDUCED and its BOILING POINT is thus increased in comparison to similar molecules.