In previous studies, the influence of moisture in perovskite systems has been predominantly regarded as a negative factor or considered only in a limited manner through its indirect effects arising from byproduct formation. However, in this study, we demonstrate that water does not merely generate species such as HCl, dimethylamine, and formic acid that assist nucleation, but can also contribute directly to the modulation of thin-film properties, including the control of interfacial characteristics.