Water is dipolar. Water (H2O) is the most abundant molecule on Earth's surface, constituting about 70% of the planet's surface - one molecule of water has two hydrogen atoms covalently bonded to a single oxygen atom.
Oxygen attracts electrons much more strongly than hydrogen, resulting in a net positive charge on the hydrogen atoms, and a net negative charge on the oxygen atom. The presence of a charge on each of these atoms gives each water molecule a net dipole moment.
In chemistry, the dipole moment is a quantity showing the extent of a system's polarity, that is, the degree to which electric charge is unevenly distributed throughout the system. Individual covalent bonds also possess dipole moments. In the latter case, the dipole moment is defined as the product of the net partial charge difference between the two bonded atoms and the distance between them. The magnitude of the dipole moment is commonly measured in debyes, while its SI unit is the Coulomb-metre.
Electrical attraction between water molecules due to this dipole pulls individual molecules closer together, making it more difficult to separate the molecules and therefore raising the boiling point. This attraction is known as hydrogen bonding. The molecules of water are constantly moving in relation to each other, and the hydrogen bonds are continually breaking and reforming.
A water molecule can form a maximum of four hydrogen bonds because it can accept two and donate two hydrogen atoms. Other molecules like hydrogen fluoride, ammonia, methanol form hydrogen bonds but they do not show anomalous behavior of thermodynamic, kinetic or structural properties like those observed in water. The answer to the apparent difference between water and other hydrogen bonding liquids lies in the fact that apart from water none of the hydrogen bonding molecules can form four hydrogen bonds either due to an inability to donate/accept hydrogens or due to steric effects in bulky residues.
