An electrokinetic device is capable of operating for extended periods of time, e.g. days to a week, without producing significant gaseous byproducts and without significant evolution of the pump fluid. Features of the electrokinetic device include: the electrodes in the electrokinetic device are capacitive with a capacitance of at least 10.sup.-4 Farads/cm.sup.2; at least part of the inner surfaces of the electrodes have an area greater than the effective area of the porous dielectric material; at least part of the inner surfaces of the electrodes have a current flux less than 20 microamperes/cm.sup.2; and at least part of the inner surfaces of the electrodes have a current flux that varies by less than a factor of two. The electrokinetic device can have one or several of these features in any combination.