Source/sink is a source or sink of water per unit area in 2D [m³/(m²*d)]. Thus in 2D horizontal models it is suitable to be used as the parameter for groundwater recharge. In 3D models, source/sink is also available. Here, however, it is a source or sink of water per unit volume [m³/(m³*d)], which is not directly applicable for groundwater recharge. Therefore in 3D models, there is an additional parameter "In/outflow on top/bottom" for groundwater recharge. The latter can only be set on the top layer for infiltration from top and on the bottom layer for inflow from a deeper aquifer.
