We verified the origin of water-infiltration-induced electricity generation by an ionovoltaic effect, specifically, ion–surface interaction induced potential asymmetry in porous structures. When 20 μl of water (NaCl, 0.1 M) infiltrates into a porous CuO nanowire film, electrical power of ～0.45 V and ～0.23 μA is produced for 40 minutes. Moreover, a method of proportionally amplifying electricity is presented, and the practicability is shown by turning on an LED with infiltration of eight seawater droplets.