A damage-free dewatering method, without centrifugation, mechanical squeezing, and solar irradiation, is important for separating solids from pure water and can be used for the production of biomass-derived renewable fine chemicals, fertilizers, and fuels in biotechnological applications. Herein a damage-free steam generator constructed by a single sheet of nitrogen-doped nanoporous graphene and nitrogen-doped porous graphene foam as hierarchical structures is reported. The multifunctional hierarchical graphene steam generator has a high water evaporation rate (1.54 kg m(-2) h(-1)) accompanied by a high energy conversion efficiency (82.2%). Furthermore, it exhibits excellent persistence in dewatering performance over multiple uses, unlike the graphene foam that shows marked reduction in performance after several reuses. Therefore, the multifunctional hierarchical graphene steam generator is a cost-effective material for accelerating both the harvesting of biomass concentrates and the production of pure water.