Covalent bond
A water molecule consists of one oxygen atom and two hydrogen atoms held together by a covalent bond. In this case the oxygen atom shares one electron with each hydrogen atom. This means that the oxygen atoms has a small net positive charge and the hydrogen atom has a small net negative charge. As a result, the oxygen and hydrogen atoms are attracted to each other due to the electromagnetic force. Because of this the water molecule is a polar molecule: its charge is not evenly distributed.