No, water does not effect gravity.
Place a weighing scale underwater, and then a 10 pound lead weight on that scale and you will see that the 10 pound lead weight still reads as 10
pounds under water.
The whole flotation thing is an illusion of weightlessness because the water is more dense, and the air in our bodies for instance helps to keep us
afloat.
You've got altering density all wrong too.
I can alter the density of a pot of water, turning it into a gas by boiling the water.
this is called a phase change, or state change.
quite a number of materials can go through this process of altered density from solid, to liquid, and gas through application of heat, or pressure.
You can take common breathing air and increase it's density through application of pressure until it becomes liquid air.
You can do also change the density by heating it up.
Please, revisit your high school science lessons, and also please consider that many many many many people smarter than you, or me, or anyone else on
this forum have been trying to solve the problem of "...", and because they haven't done so yet, I'm extremely skeptical that you will either.
Tell you what, visit arxiv.org. Read some papers on gravitation.
For instance, here's just one. Keep your eye on the Math.
Unification of Electromagnetism and Gravitation in the Framework of General Geometry
Abstract
A new geometry, called General geometry, is constructed. It is proven that its the most simplest special case is geometry underlying Electromagnetism.
Another special case is Riemannian geometry. Action for electromagnetic ﬁeld and Maxwell equations are derived from curvature function of geometry
underlying Electromagnetism. It is shown that equation of motion for a particle interacting with electromagnetic ﬁeld coincides exactly with
equation for geodesics of geometry underlying Electromagnetism. It is also shown that Electromagnetism can not be geometrized in the framework of
Riemannian geometry. Using General Geometry we propose a uniﬁed model of electromagnetism and gravitation which reproduces Electromagnetism and
Gravitation and predicts that electromagnetic ﬁeld is a source for gravitational ﬁeld. This theory is formulated in four dimensional spacetime and
does not contain additional ﬁelds.
Here;s the root to arxiv:
arxiv.org
There's plenty papers on Physics, Astro-physics, Theoretical Physics, as well as Math, and tons of really really fun stuff on the bleeding razor sharp
cutting edge of scientific research.
After you're done reading the full paper I've listed above, not just the abstract, please come back and tell us what you've learned. I picked a
really super short and simple paper for you too, so, you should have loads of stuff to tell us about when you're done.
edit on 8-4-2012 by nineix because: (no reason given)