A current passed through a solution of (primarily) water and an
electrolyte will produce hydrogen "H" and "O" Oxygen at a ratio of one
part hydrogen to two parts oxygen.  If the hydrogen is collected and
subsequently burned the product of that combustion will be heat, and
water.  My question relates to the water. That question is this: "Will
there be the SAME amount of water left as the water that was
'consumed' during the electroysis?  Given that energy is neither
created nor destroyed, my feeling is that here there would be an
equilibrium whereby the water consumed, and the water remaining
FOLLOWING the process would be the same.
The purpose in asking this question is to (in my own mind) determine
if, for example, usinf freely available solar electgric panels and
electrolysis, if indeed one would actually achieve a virtually ZERO
impact on the environment.
If the water 'consumed' vs the water left over AFTER the above
reaction is indeed the same, then I would be inclined to say yes. In
othter words, would we, or would we NOT be DEPLETING what is
essentially a non-renewable resource, i.e. WATER!  This is a question
that has plagued me for some time and I haven't been able to find an
answer (yet) on my own.  Its possible that nobody has considered  it
because we may simply assume that the availability of H20 on this
planet is infinite.  I think not.  I don't have a sufficiently
sophisticated scientific background to deduce this perplexing
question.  I hope its not a 'stupid' one.
Can you help?

punkycry

Your feeling is correct 
  " the water consumed, and the water remaining
FOLLOWING the process would be the same" 

and the question in neither new nor stupid.

 We actually had it here on GA already:
http://answers.google.com/answers/threadview?id=456343
and, as explained there, answer is :
       use of hydrogen will not deplete water resources.

It is important to differentiate between 'source of energy'
and 'store of energy'. 
Today, gasoline is used as both: store and source of energy for cars.
In the near future these two functions will be separated. Store will be
hydrogen or electric battery. It will actually 'save lot of energy' since
to produce energy in a power plant (to charge a battery and then to
run electric motor) is much more efficient then running the motor
(steam engine) directly, from a fossil fuel.

We are using these terms in a loose, everyday sense. If we would want to
be scientifically accurate, we would have to add few corrections 
(which however do not change the conclusion), such as:
"Oxygen at a ratio of one part hydrogen to two parts oxygen"  would be
"Oxygen at a ratio of two parts hydrogen to one part oxygen"

It is H2O not HO2

We should not say we 'produce energy from a source', such as coal since
energy cannot be created or destroyed.

Second part of the comment by qed100-ga is not correct. Imagine a waterfall.
Without a waterwheel, all it's energy is dissipated as heat. A man builds
a waterwheel, runs a generator, charges a battery and later uses it to
run a microwave to  cook a chicken... etc
In the end, the same energy will be dissipated as heat 
(not counting the chicken :-) or counting it properly in both cases.
 So, in conclusion:
 Earth energy balance is not altered by using renewable resources (with some
qualifications, like balancing deforestation with reforestation to keep same
concentration of carbon dioxide in the atmosphere, etc).

It is also important to understand the difference between energy and usable
energy. What is energy anyway?

          "Energy is the ability to do work" ??

 I do not like this definition.
 It begs a question: what is work?  (applied energy?)
as discussed here:
http://answers.google.com/answers/threadview?id=475235

Rating appreciated  Hedgie

Having subjected quantity W of water to electrloysis, decomposing it
to hydrogen & oxygen, if the collected H & O are allowed to combine
chemically the result will be the exact quantity W that the system
started out with. So no, in that sense water will not be lost from
Earth's H2O cycle. (This is that the H & O are recombined. If they are
kept stored as separate elements, then of course the total amount of
water in the world will be lessened.) The recombination also yields
the same electrical energy that was required to break down the H2O.

   However... due to heat losses in the generating system, it takes
more energy to generate the original electrolytical current than is
carried by the current itself. It's also an unfortunate fact that, at
least at this time, the useful energy deliverable by a photovoltaic
(solar panel) is less than the energy of its own manufacture. So the
electrolysis of water is a negative source of energy.

   But even that aside, it's not possible to have a source of
domesticatable energy with zero environmental impact. Harnessing
hydroelectric energy diverts energy from the water cycle somewhere
along the line. The same goes for wind power. Capturing solar energy
steals from both hydro and wind. To keep environmental impact
tolerable, use of these forms of energy must be kept to a negligible
level. This means keeping it either at a level comparable to normal
natural fluctuations, or keeping the increases in wattage usage slow
enough to be adapted to by Earth's temperature regulating system.

   Exploitation of stored energy, such as the chemical energy in
combustibles, geothermal, or the nuclear energy in fissile materials,
means dumping that heat into the environment at a rate faster than if
left alone. If the use of this form of energy is too high, then there
is the risk of overtaxing the regulating system.

   My point is not to be pessimistic. It's just that it's a fact that
energy is never free, and never clean. Every generation steals from
its own children.

While hedgie is correct in stating that the use of an energy source
such as a waterwheel doesn't alter the end effect in terms of the
total heat lost, this does not invalidate qed100's point. The energy
available is being diverted away from its natural course, and this can
have serious environmental consequences. For instance, some of that
kinetic energy may have previously performed an important mixing
function. If enough of it is diverted, some parts of the river may
become stagnant and the ecosystem can fail at some points.

Something similar but more extreme is the diversion of river water for
irrigation use. This is a highly contentious issue in many parts of
the world. You could argue as hedgie does that there's been no net
change to the amount of water used, but that isn't going to pacify the
people downstream of you whose river has suddenly dried up since you
built your dam.

Hedgie's example is in fact exactly the same, except that instead of
the water itself being the resource used, it is the kinetic energy of
that water. The same principle applies: the more you remove from it
upstream, the less is available downstream. Granted, immediately
before a waterfall is not so bad since a large amount of it is about
to get lost anyway, but it doesn't mean there's no impact.

Manuka, 
         I do not intend to engage in protracted debate on this. Not that it
is not important or interesting, but because there are other fora for
this and issue raised is not a well defined technical point. So, just
briefly:
 
 I did not say 'waterwheel has no impact', only that both water and
energy is conserved. The Qed-ga's statement I was reffering to is
  " It's just that it's a fact that
energy is never free, and never clean. Every generation steals from
its own children."

 Which seems to say: We cannot have a steady state eco-system which includes
people. 

Such statement would not be correct. Such situation is unlikely with modern
civilisation, but is not impossible. For example, one can argue that
american indians before 1400 AD lived in a dynamic equilibrium with
nature, and each generation had similar conditions as previous one.
Hedgie

you are right in your thought process punkycry-ga , but the problem is
hydrogen is explosivly combustible and we are unable to make engines
which can convert the energy released by combustion of hydrogen to
usable mechanical energy..like the one used to run Cars and Trains.
                                                regards

I beg to differ with the last comment. Both internal and external
combustion engines can be run on hydrogen quite successfully without
problem. Hydrogen is no more explosive (dangerous to handle or store)
than any of the other fuels now commonly used. Many were considered
dangerous and explosive at the time of there introduction.....tanks of
flammable and explosive gasoline barreling down our streets at 15
MPH......

qed100 perpetrates the outdated myth that PV consumes more energy than
it delivers.  This may have been true in the distant past, but PV has
made huge strides in manufacturing technology, particularlly in
consumption of silicon.

 There are many references on this subject for example
http://jupiter.clarion.edu/~jpearce/Papers/netenergy.pdf
which confirm that PV produces back 5-30 times more energy than needed
to produce and instal them

Interesting Michelin contends that 50m2 of PV on the roof is enough to
generate enough hydrogen to drive 20 000km/y  with a fuel cell car ...
distributed generation of auto fuel - that would be a revolution