A hydrogen bond is an attractive interaction between a hydrogen atom from one molecule and an electronegative atom (such as oxygen, nitrogen, or fluorine) from another molecule. In the case of water, the electronegative atom is oxygen. The oxygen atom in water has a partial negative charge, while the hydrogen atoms have a partial positive charge. This allows the hydrogen atoms of one water molecule to form hydrogen bonds with the oxygen atoms of another water molecule.

The ability of water to form hydrogen bonds with itself is responsible for many of its unique properties, such as its high surface tension and high specific heat capacity. Hydrogen bonding also allows water to dissolve many substances and to form solutions.