Solar interfacial evaporation is a promising technology for the purification of seawater and polluted water using sustainable solar energy. An adjustable shape and internal-channel size of photothermal evaporation material are essential for regulating heat utilization and water supply rate to three-dimensional (3D) evaporation device. However, a simple method for the preparation process is rarely reported to date. Inspired by bread making, a straightforward fermentation method is applied to the preparation of adjustable porous hydrogel as photothermal evaporation materials. It only takes 40 min to ferment and three simple freeze-thawing cycles to construct the final hydrogel materials. A mold can be used to easily adjust the external shape of the fermentation porous hydrogels (FPHs). The internal-channel size of FPHs can be simply tuned by the fermentation time. The flexible porous structure endows FPHs with excellent photothermal evaporation capability and makes it easy to meet the requirements of water supply rates under the light intensity of different latitudes for water treatment.