A refrigerator appliance or a variable shelf assembly, as provided herein, may include a selectively-sealed shelf tube, a support piston, a shelving bracket, a first valve, and a second valve. The selectively-sealed shelf tube may define a fluid inlet to receive water therethrough and a fluid outlet to exhaust water therethrough. The support piston may be slidably disposed within the selectively-sealed shelf tube to move between a top position and a base position according to a volume of water within the selectively-sealed shelf tube. The shelving bracket may be fixed to the support piston to move therewith. The first valve may be upstream from the fluid inlet to selectively permit water thereto. The second valve may be downstream from the fluid outlet to selectively permit water from the variable shelf assembly.