The hydrogen bonding of interfacial water in the vicinity of different surface imperfections of Pt(100) surfaces was analysed from trajectories obtained from molecular dynamics simulations. Two alternative H-bond definitions-an energetic and a geometric-were used. We found that the number of hydrogen bonds for water molecules at different surface imperfections decreases as the number of neighbouring platinum atoms increases, although the number of neighbouring water molecules does not always decrease in a parallel way. Thus the effect of surface imperfections can be explained partly in terms of geometric reasons, but our analysis showed that the ordering effect of the platinum atoms also plays an important role. In certain positions at step edges there exist water pairs with stable configurations but with positive pair energies. Their existence is obviously due to the ordering effect of the platinum surface. These water pairs were found to have a very symmetrical arrangement pointing with their hydrogens almost towards each other.