Block not floating on custom-made water?

Hi, I tried to make a custom-made water in my game, and I have a block in my workspace. I know that heavy parts float on water, because it's volume is more than the water's volume, making it less dense than the water.

I used the PhysicalProperties class, and set the water's density to 1, and the other part's density (a part that is plastic-materialized) to .7 . I make the water's size rise in the game, and the part doesn't seem to float when it's unanchored.

Why is that?