Developing a highly efficient system for solar steam generation (SSG) using a straightforward and eco-friendly method to harvest freshwater is fascinating but challenging. Here, we stir the mixture of brewed tea and HAuCl₄ to prepare Au nanoflowers, possessing broad wavelength light absorption and excellent photothermal effects. After freeze-drying the mixture of Au nanoflowers, cellulose nanocrystals (CNCs), and aqueous polyurethane (PU) emulsion, we obtain three-dimensional (3D) porous structures (CNC-PU-Au) for SSG. The whole process does not involve any sophisticated procedure or produce detrimental by-products. The evaporation rates are 2.24 kg·m⁻²·h⁻¹ for pure water and 2.18 kg·m⁻²·h⁻¹ for seawater using CNC-PU-Au under one sun. The solar energy conversion efficiency is up to 90.92% under one sun illumination. Besides, CNC-PU-Au shows self-driven salt resistance and durability. In outdoors application for seawater desalination, the maximum evaporation rate can maintain at 2.19 kg·m⁻²·h⁻¹ in spring and 3.42 kg·m⁻²·h⁻¹ in summer. These unique features promise the utility of CNC-PU-Au in the eco-friendly water treatment industry.