Water has been labeled as a devil in fabrication and stability of perovskite solar cells. The inherent cognition impels researchers to prepare perovskite films in water-controlled conditions. Herein, water is used as a green solvent to prepare CsPbBr films through a two-step spin-coating method. Due to the high solubility of CsBr but low solubility of PbBr in water, it provides a possibility to deposit CsBr onto PbBr from water solution without destroying the film. Here, high-quality CsPbBr films are fabricated by spin-coating concentrated CsBr/HO solution onto the PbBr film followed by annealing. As a result, the solar cells basing on a configuration of FTO/TiO/CsPbBr/Carbon exhibit a power conversion efficiency of 6.12%. This work provides a simple and easy way to prepare high-quality CsPbBr films for efficient solar cells. It makes a solid step toward reducing the solvent toxicity in the fabrication process of perovskite solar cells. It also breaks the forbidden zone for fabricating perovskite films from water and updates the inherent understanding of water in the research study of perovskite solar cells.