Protein-protein recognition regulates the vast majority of physiological or pathological processes. We investigated the role of hydration in collagen recognition by bacterial adhesin CNA by means of first principle molecular-dynamics samplings. Our characterization of the hydration properties of the isolated partners highlights dewetting-prone areas on the surface of CNA that closely match the key regions involved in hydrophobic intermolecular interactions upon complex formation, suggesting that the hydration state of the ligand-free CNA predisposes the protein to the collagen recognition. Moreover, hydration maps of the CNA-collagen complex reveal the presence of a number of structured water molecules that mediate intermolecular interactions at the interface between the two proteins. These hydration sites feature long residence times, significant binding free energies, and a geometrical distribution that closely resembles the hydration pattern of the isolated collagen triple helix. These findings are striking evidence that CNA recognizes the collagen triple helix as a hydrated molecule. For this structural motif, the exposure of several unsatisfied backbone carbonyl groups results in a strong interplay with the solvent, which is shown to also play a role in collagen recognition.