Is it true that pure water (100% H20) is poisonous, undrinkable or
harmful to your health?

Well, it can kill you if you drown in it...

Pure water is without any minerals.Hence its tasteless and not really
good to drink.However it is not poisonous nor life threatning.

But as it is without any minerals it serves no real purpose to our
Cellular nutrition.

100% pure water is not, in the SHORT term, poisonous, undrinkablr or
harmful to your health.  Pure water is that which has not mineral
content.  For example, water that's been through an RO filter (reverse
osmosis) or that has been distilled is generally devoid of all
minerals.  As I stated earlier, drinking such water in and of itself
is not problematic, but the lack of minerals can have several
consequences.  First, let's talk about osmosis. If you chronically
expose your tissues (say in your gut) to distilled water you will end
up disrupting nutrient uptake in your gut, in particular of salts such
as iodine.  This can lead to hyerthyroidism and other disorders.  Now,
if you drink distilled water while eating a bag of potato chips, or
any other food with a high salt or mineral content, I can assure you
that the distilled water will have little effect as the salt on the
chips will more than compensate for the lack of salts in the distilled
water.  So, ultimately the toxicity of distilled water can be best
asessed in the context of what else you consume.  In general, however,
I would say that drinking distilled water is not a particularily good
idea.  IF you search the internet  (for example, for go
www.mercola.com/article/water/distilled_water_2.htm ) you will find
that some nutritionists (especially those into holistic medicines)
will recommend drinking distilled water to help detoxify your body.  I
would argue that drinking a good bottled water (replete with minerals)
would do a better job at detoxification becuase it will promote
metabolite and nutrient uptake by your stomach and gut while promoting
waste product elimination by your kidney.

If you think this is a good start, let me know and I'll  send you some
more links for your perusal.  Does this answer your question?

Thanks deepseep, that sounds correct I think I just lost my Bet.
Perhaps I was thinking of De-Ionised water or somthing....

Things in solution tend to distribute evenly in that solution. Water
does this also, a process called osmosis. Your cells in your body are
surrounded by a semi-permeable membrane, which means that water can
pass into and out of your cells, while most other ions cannot. If on
the outside of a cell there is 100% water, and the other side is
cytosol (cellular fluid full of ions and protiens), more water will
enter the cell in an attempt to balance out the "concentration" of
water on both sides. So, in theory, your cells could lyse (burst) by
abosrbing too much water. Drinking this water will probably not have
any adversie effects, as your stomach is full of ions and also
constantly produces more HCl to keep a constant pH. However, I also
would not drink too much. More dangerous would be immersing yourself
in pure water. That would probably cause some damage to your skin
cells if you stay in long enough.

Perhaps the rumor that pure water is toxic comes from this elaborate spoof:

http://www.dhmo.org/facts.html

It would drain the calcium for the body.

Now for the truth:
1.  You won't find any scientific papers/reports demonstrating that
pure water is harmful for REGULAR day-to-day consumption or that it
leaches minerals out of the bones.  That should say something by
itself.
2.  When the Navy needs water on their submarines, they use
desalinators and distillers.  The Navy has used purified water for
over 50 years.
3.  If a doctor tells you that you have low calcium, does he tell you
to drink more mineralized water?  No, of course not; he tells you to
drink milk or add dairy products (read food) to your diet.  This
clearly demonstrates that we rely on food for our mineral intake.
4.  If I were to ask you what minerals your current tap water has in
it and also ask what amounts, would you be able to tell me?  No,
because you would have to have your water analyzed daily to know.  How
can you rely on getting minerals from something that you don't even
know has minerals?
5.  Your body has several mechanisms in place to maintain homeostasis.
 Therefore, drinking acidic water or alkaline water should make no
difference as the body will try to equal the PH.
6.  There's a lot of mis-information on the web and in print about
drinking purified water.  The only times it could be of danger is if
you had some serious medical problem or if you ONLY drank purified
water AND did not consume any or at least very, very little food!  Of
course, you would suffer from protein, amino acid, vitamin and mineral
deficiencies.