The composition and polar covalent nature of water allow water molecules to form what

hydrogen bonds

Explanation:

Hydrogen bonding (H-bonding) is an intermolecular force having partial ionic-covalent character. H-bonding takes place between a hydrogen atom (attached with an electronegative atom e.g. O, N and F) and an electronegative atom (O, N and F).

Hydrogen bonding generally appears in covalent molecules.

In , O is a highly electronegative atom attached to a H atom through a covalent bond. Therefore oxygen atoms gets partial negative charge and H atoms gets partial positive charge.  

Hence  polar covalent nature of water allow water molecules to form hydrogen bonds.