The geothermal reservoir at Waiwera has been subject to active exploitation for a long time. However, the continuous production of geothermal water, to supply hotels and spas, had a negative impact on the reservoir. The aim of this work was to link the influence of the abstraction rates to the measured water level data to derive reservoir properties. For the analysis, a modified deconvolution algorithm was implemented and shown to be applicable and in accordance to results of a pumping test.