The equation relating potential energy to
kinetic energy is:

mdg=mvv/2

where m=mass
d=height
g=gravitation const.
v=velocity

NOTE: THAT m(MASS) CANCELS OUT!!!!!!

height=velocity squared/2*gravitational const

OK an example: Say we throw a glider vertially
in the air. How high will it go if its initial
vertical speed is 140mph. Approximately 660feet.

OK. Now lets throw the same glider vertically at
the same speed and measure how high it rises for
its vertical speed to have diminished to 50mph,
575 feet!

So if you fly your glider at 140mph and you
efficiently pull the stick back and climb
until you reach 50mph you will gain over 500
feet. Conversely if you are flying at 50mph
and push the stick forward until you accelerate
to 140mph you will lose about 600 feet. Why
500 feet and 600 feet and not 575 feet? Because
you don't have a 100% efficient flying machine!

OK. Same glider with and without water. Should
you expect the same result going from one speed
to another? No! But the difference will be small
usually and will depend on the glider's polar.
If the 2 speeds are on the linear part of the
polar (ie close to best glide) the difference
will be negligible. If you select the 2 speeds
at the high end of the polar water wins. At
the low end water loses. VNE to full stall -
your guess is as good as mine!

I encourage all of you to use the above equation
with your own numbers. Remember the v squared
term is the differance of 2 squares. Example:
140*140-50*50. Also be consistent in your use
of terms - metric/English/whatever.

Dave