ABSTRACTThe upconing of saline water in response to pumping from an overlying layer of fresh water is investigated by numerical integration of the governing differential equation. The transition zone between the fresh and saline water is idealized as an abrupt interface. Full consideration of the nonlinear boundary conditions on the water table and interface surfaces is included for steady flow toward partially penetrating pumping wells in both isotropic and anisotropic aquifers. There exists an optimum well penetration into the fresh‐water layer which permits maximum discharge without salt‐water entrainment. The optimum penetration increases as the vertical permeability is reduced relative to the horizontal permeability. The maximum well discharge obtainable without salt‐water entrainment is greater for aquifers with a reduced vertical permeability than for isotropic aquifers, a result that contrasts with previously published conclusions. Previous analyses which linearize the boundary condition on the interface overestimate the critical disc