Water is a compound that contains the elements hydrogen and oxygen and is connected by covalent bonds.
The compound which can donate an electron pair to an acceptor compound is known as Lewis base.
In a water molecule, oxygen has 6 valence electrons and therefore requires 2 additional electrons from 2 hydrogen atoms in order to complete its octet.
Thus there are two pairs of lone electrons on an Oxygen atom that are not bound to any other atoms.
Since the Oxygen atom contains a lone pair of electrons, the water molecule is an example of a Lewis base.