Are you sure? What guarantees that the water containers will stay horizontal? If both have the same weight they could be in either position, unless the bar works like a scale and has an inherent tendency to be horizontal. However that would mean that if you push one of the water containers down (which is what you'd do if you forcefully submerge the ball - the buoyant force will push the ball up but also the water down) some force will be generated at the water-bar mounting point that will make the umbrella fall. The whole apparatus, ignoring it's complete technical infeasibility, would only work if the water tanks were mounted on the ground, not on the umbrella itself.
E: Ah I see if they were connected they'd try to be horizontal by themselves.
Goddamn this whole idea is such a load of crap why am I even wasting time with this.