We have studied the effect of adsorbed water on the primary photocarrier-generation process in Y-form titanyl phthalocyanine (Y-TiOPc) by using ground:state absorption and time-resolved fluorescence spectroscopy. The water adsorption is the unique feature of Y-TiOPc, which is not observed in the other polymorphs of TiOPc. We report for the first time the water-induced change of the absorption spectrum, that is, the hydrochromism of Y-TiOPc. The fluorescence lifetimes and amplitudes of Y-TiOPc are greatly influenced by adsorbed water. We have found that the mechanism of the fluorescence quenching of Y-TiOPc caused by water adsorption is the same as that by an electric field. Adsorbed water enhances the photocarrier generation of Y-TiOPc in the same way as an electric field does in the picosecond time regime.