Two problems of rotation of a liquid in crossed electric and magnetic fields are formulated and solved as applied to the study of the principles of the interaction between external electric and magnetic fields and weakly conducting water type liquids (running water, sea water) and their solutions (σ ~ (10–2–102) Ω–1 m–1). In the first problem, the liquid is contained in the gap of a vertical cylindrical capacitor, while the second problem deals with the liquid in a rectangular cuvette, two lateral vertical walls of which are used as armatures of a planeparallel capacitor. In either case, a constant vertical magnetic field is applied to the liquid, while a constant voltage is maintained between the armatures of the capacitor. Three sets of boundary conditions are considered in the first case: the capacitor is of infinite length (throughout the height); the capacitor is confined by a solid bottom from below and has a free boundary with the atmosphere at the top; the capacitor has closed ends and the liquid occupies the entire capacitor gap. The results can be used in various practical applications, for example, for pumping of weakly conducting liquids.