In an electric field, water develops a specific pressure that pushes in all directions and can result in an eternal (limited only by the deterioration of the system) motion, on condition that the system provides suitable channels for water to move through. If, in the simplest case, two opposite charges immersed in water are close enough to attract each other, the specific pressure that develops between them counteracts the force of attraction and the latter apparently decreases:
"However, in experiments in which a capacitor is submerged in a dielectric liquid the force per unit area exerted by one plate on another is observed to decrease... [...] This apparent paradox can be explained by taking into account the DIFFERENCE IN LIQUID PRESSURE in the field filled space between the plates and the field free region outside the capacitor." http://farside.ph.utexas.edu/teaching/jk1/lectures/node46.html
Tai Chow, Introduction to Electromagnetic Theory: A Modern Perspective, p. 267: "The strictly electric forces between charges on the conductors are not influenced by the presence of the dielectric medium. The medium is polarized, however, and the interaction of the electric field with the polarized medium results in an INCREASED FLUID PRESSURE ON THE CONDUCTORS that reduces the net forces acting on them." http://www.amazon.com/Introduction-To-Electromagnetic-Theory-Perspective/dp/0763738271
The specific pressure that develops in water placed in an electric field is NON-CONSERVATIVE. This means that, if suitably harnessed, the pressure will do work AT THE EXPENSE OF AMBIENT HEAT (in violation of the second law of thermodynamics). Here is a simple example:
When the plates contact the liquid's surface, a force in the upward direction is exerted on the dielectric liquid. The total charge on each plate remains constant and there is no energy transferred to the system from outside." [END OF QUOTATION]
There IS energy transferred to the system from outside. The rising water can do work, e.g. by lifting a floating weight, and this work can only be done at the expense of AMBIENT HEAT.
What is the molecular mechanism behind the effect? Here is a schematic presentation of water dipoles in the electrical field:
If it were not for the indicated (with an arrow) dipole, other dipoles in the picture are perfectly polarized as if there were no thermal motion. Of course, this is an oversimplification ? thermal motion is a factor which constantly disturbs the polarization order. The crucial point is that, as can be inferred from the picture, any thermal disturbance contributes to the creation of a pressure between the plates. Consider the indicated dipole. It has just received a strong thermal stroke and undergone rotation. As a result, it pushes adjacent dipoles electrostatically, towards the plates. Macroscopically, the sum of all such disturbances is expressed as a pressure exerted on the plates. One can also say, somewhat figuratively, that the indicated dipole has absorbed heat and now, by pushing adjacent dipoles, is trying to convert it into work.