(Review material: Visit the MIT Hypertextbook)

Water has a dipole moment

http://esg-www.mit.edu:8001/esgbio/chem/H2O2.gif

Hydrogen bonding of water molecules

From the MIT Hypertextbook: Hydrogen bonds have polarity. A hydrogen atom covalently attached to a very electronegative atom (N, O, or P) shares its partial positive charge with a second electronegative atom (N, O, or P). One example, involves the hydrogen bonding between water molecules. More examples: H | R--O--H ||| N--R R==N--H ||| O==R | Note that R stands for H any side group. Hydrogen bonds are ~5 kcal/mol in strength. These bonds are frequently found in proteins and nucleic acids, and by reinforcing each other serve to keep the protein (or nucleic acid) structure secure. But, since the hydrogen atoms in the protein could also H-bond to the surrounding water, the relative strength of protein-protein H-bonds vs. protein-H2O bonds is smaller than 5 kcal/mol.