If a constant-charge parallel-plate capacitor is totally immersed in
water, the force of attraction between the plates is 80 times weaker
than the force of attraction in vacuum. However, if we thrust some
solid dielectric between the plates (not necessarily occupying the
whole distance between them - it could be rather thin), the force of
attraction becomes even greater than in vacuum. Accordingly, the
following four-step cycle (carried out very slowly) violates the
second law of thermodynamics:

1. Plates are immersed and fixed. We thrust the solid dielectric.
2. Plates get closer. We GAIN work.
3. We withdraw the solid dielectric.
4. Plates get apart; initial state restored. We SPEND work.

When the plates are immersed in a liquid dielectric (water), some
additional pressure between them emerges, pushes them apart and so
counteracts their electrostatic attraction (W. Panofsky, M. Phillips,
Classical Electricity and Magnetism, Addison-Wesley, Reading,
Massachusetts (1962), pp. 111-116). If the plates are vertical and
only partially immersed, the same pressure forces the liquid between
the plates to rise above the surface of the water pool (see fig. 6-7
on p. 112 in Panofsky's book). What if one punches a small hole in one
of the plates, just above the surface of the pool? Will the lifted
water leak through the hole and fall? If lifting is due to an
additional pressure generated within the bulk, as assumed by Panofsky
and Phillips, then water WILL leak through the hole and the second law
will be violated. No matter how weak the waterfall is, in principle it
can rotate a waterwheel...

The perpetuum mobile of the second kind described above will never
become a money-spinner and will not solve the energy problems of
humankind. However Nature may occasionally have used such (inefficient
from an anthropocentric point of view) mecanisms and the knowledge of
them could make us unexpectedly rich in some unconventional sense.

Pentcho Valev