We study the interaction of water with oligo(ethylene glycol) (OEG)-terminated alkane thiolate self-assembled monolayers (SAMs) in the helical and the planar "all-trans" form with ab initio methods to determine the stability and density distribution in water clusters as a function of molecular conformation. We find that the amphiphilic behavior of the OEG moieties depends on their molecular conformation and that the energetics of water adsorption is dominated by electrostatic interactions. The SAM surface of helical OEG provides a template for water nucleation, whereas water is not stable on a surface of planar OEG strands. These results suggest that protein resistance of OEG-terminated self-assembled monolayers is a consequence of the stability of the interfacial water layer, which prevents direct contact between the surface and the protein.