Liquid water has many peculiarities which confer special properties. The most important among them probably are the ability to establish hydrogen bonds, a high polarity and a high dielectric constant. In the presence of liquid water, large organic molecules have to manage the conflict between hydrophobic groups and hydrophilic groups. This duality can generate interesting prebiotic situations such as the stereoselective aggregation of short peptide sequences of alternating hydrophobic-hydrophilic residues into thermostable beta-sheets endowed with chemical activity. Liquid water is also a powerful hydrolytic agent. As such, it allows pathways which would have few chances to occur in an organic solvent.