A nonporous crystalline organic cage (Oba-cage) effectively captures and stores water from a mixed organic solvent/water system. The observed water uptake capacities of 106.2 mg g−1 (10.6 wt%) at 0 °C and 102.1 mg g−1 (10.2 wt%) at 25 °C are significant for nonporous cages, as collectively confirmed by different techniques. This excellent water uptake and storage performance is attributed to the strong host–guest O–H/N hydrogen bonding interactions between the imine nitrogen atoms of the cage and water molecules. These findings establish organic cages as a promising class of compounds for water harvesting and storage applications.