Electrowetting of electrolyte droplets and flows on flat and rough surfaces were studied using the lattice Boltzmann model. Hysteresis and saturation of the contact angle in electrowetting were observed, and this behavior was much more amplified for the rough surface. On a rough surface, the existence of wide grooves will result in saturation of the contact angle. Alternatively, if there are narrow grooves that can be bridged by the droplet, the contact angle will change with discrete jumps and will exhibit hysteresis. We show that the flux across the channel can be effectively controlled by the external voltage in a rough-wall channel. (C) Koninklijke Brill NV, Leiden, 2011