Marble has a density of 0.098 lbs/in^3^. So a 500lb sphere has a volume of 500lb/.098lb/in^3^= 5102 in^3^. That gives a radius of (5102 in^3^ * (3/(4pi)))^(1/3)^= 10.68 in.

Let’s say the bowl it sits in has 2/3 the radius. So 7.12in. That makes the enclosed surface area pi*( 7.12in) ^2^= 160in^2^. So 500lbs/160in^2^ = 3.14 psi. How fast do you think the water will spray out at 3.14 psi? Without any drag, out of an ideal nozzle, it would be 6.5mph. However, the pressure will actually be higher in the middle and tapers off to 0 at the edge thanks to the flow diverging and drag. So really the pressure drop at the opening is even smaller.

There’s a lot of lifting area which means you don’t actually need much pressure. You can lift entire buildings with large water bags.