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The contact electrification voltage is measured when a colloidal probe is released from a substrate at different relative humidity levels. Varying the geometry of the probe and the wettability of the probe and substrate reveals that the contact electrification voltage increases with humidity up to 90% when a spherical colloidal probe is hydrophilic. These results pave the way for applications in which energy can be harvested from water and in the design of efficient energy devices, such as operating triboelectric nanogenerators in a contact-separation mode in high humidity conditions.