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The structure and adsorption environment of water on Pt(111) are investigated using infrared reflection absorption spectroscopy. The sample was prepared by the heat and quench technique at a heating temperature between 25 and 165 K. At 25 K, adsorbed water molecules exist as monomers and dimers, where the latter is evidenced for the first time. Upon annealing to 40 K, dimers dissociate and monomers cluster into bilayer ice at the terrace. At 105 K, a liquidlike phase is formed at the step. The liquidlike phase frozen in by quenching the surface to 25 K reveals itself measured in the measurements as amorphous ice. Until 125 K, bilayer ice at the terrace and the liquidlike phase at the step coexist. At 155 K, bilayer ice melts and the remaining molecules are converted to the liquidlike phase at the step. These phenomena are evidenced by the behavior of coadsorbed CO as a spectator molecule.