The oxygen atom in a water molecule carries a partial negative charge, and the two hydrogen atoms carry a partial positive charge. Oxygen is more electronegative than hydrogen, so in a water molecule, the bonding electrons are not shared evenly.
A water molecule is composed of an oxygen atom paired to two hydrogen atoms. The molecule is considered polar due to the uneven distribution of the shared electrons. The more electronegative oxygen hogs the electrons from the less electronegative hydrogen, resulting in partial charges on the atoms. The partial charges allow for water molecules to form hydrogen bonds with other water molecules. The hydrogen bonding in water molecules is responsible for many of the unique properties of water.