Select Pool Water object and add an Extrude modifier to it. Set the Amount = 0.
With the Move tool, move it down a little. Our Pool's bottom, wall, water are now placed as needed. You can adjust their positions further if you think so. Now we should add an outer ground as well.
Restore all the 4 viewports. Choose "Plane" as Object Type under Create Panel > Geometry >Standard Primitives category.
