Annual fluctuations of ground water levels of an aquifer are described as a consequence of water recharging periodically over a part of the aquifer. These areas can be depicted by drawing maps showing the areal amplitude distribution of the oscillation. Considering these areas as periodic (in time) surface sources, the damping and the phase of the oscillation are found analytically as functions of distance, the recharge area being an infinite strip or a circular disc. From these solutions the aquifer diffusivity can be calculated by the use of typecurves.