All-atom molecular dynamics simulations for a single molecule of Leu-Enkephalin in aqueous solution have been used to study the role of the water network during the formation of beta-turns. We give a detailed account of the intramolecular hydrogen bonding, the water-peptide hydrogen bonding, and the orientation and residence times of water molecules focusing on the short critical periods of transition to the stable beta-turns. These studies suggest that, when intramolecular hydrogen bonding between the first and fourth residue of the beta-turn is not present, the disruption of the water network and the establishment of water bridges constitute decisive factors in the formation and stability of the beta-turn. Finally, we provide possible explanations and mechanisms for the formations of different kinds of beta-turns. (C) 2004 American Institute of Physics.