The role of the supporting medium of water molecules in some protein activities is examined under different aspects as in the cases of a monomeric peptide, the basic fibroblast growth factor, of a dimeric peptide, the human neutrophil peptide 3, of a peptide that acts in non-aqueous environment, the gramicidin A dimer, of a water molecule present in the binding of a co-factor in a phospholipase peptide, and under the general point of view of the hydrophilic/hydrophobic properties described by a hydropathy scale. These examples illustrate the importance of water in the hydrogen bond formation that is, of main importance in keeping the peptide structures that cannot be defined without the water contributions. The conclusions confirm that living systems are like they are because water is an outstanding and abundant molecule present everywhere in living matter.