The probe just sent showed totally lit up surface features of Pluto. The Sun gets through.

Lit up enough to see isn't the point. Pluto is 39.42 times as far from
the Sun as the Earth, and that equates to a relative solar intensity,
less by a factor of 1554 ! We probably get more by Moonlight !

Watch the science channel. Scientists are saying this on "How the Universe Works."

Where's the hard evidence ? No one can know what's beneath the
surface.

Chemists are smarter than you think. A little research and they have it down. It is not that hard for them to get oxygen out of water when they have an important reason to do so. Right now they do not have one, since oxygen can be obtained so much more easily in other ways.

Getting Oxygen ( and therefore also Hydrogen ) from water, would
require an expenditure of energy, at least equal to the energy of
combustion, of that same Hydrogen with that same Oxygen, back into
water. This is very big time, and yielding far too small an amount to
be practical for breathing purposes.