H₂O water, is a molecule built from one atom of oxygen and two atoms of hydrogen. The atoms are arranged in a triangle with the O at the apex and the two H-atoms on the base at the other corners.

However this is only half the story for water. The O atom has "lone pairs" of electron density in a set of "bunny ears" which lie perpendicular (or 90 degrees) to the original O-H bonds.

This can be represented by placing the O in the center of a cube, with the H-atoms at the lower opposing corners, and the electron density pointing at opposite corners in the upper part of the cube.

In water the H-atoms are slightly positively charged and the electron density bunny ears are slightly negatively charged:

This polarisation of the water molecule is very important, once there is a collection of water molecules they arrange themselves so that a positive H interacts with the negative electron density of another water molecule. These interactions are called hydrogen bonds, hydrogen bonds are 90 percent ionic (charges interacting) and 10 percent covalent (quantum mechanical mixing of electrons).