Reactor water

our little box has a mass of 5, low enough so it can float ...

you can drop or push the box onto the water, or release it from the depths.

tip – in the preview window, using the right mouse button, you can pick up an object either from the objects edge, or the COM.

Make a plane if you want to see the water in a render. it needs enough segments to deform. then use good old bind to space warp and drag from your plane to the water object.