1. A method of calculating the flow rate through a pumping station having a pump, comprising the steps: (a) storing in a memory means a table correlating pumping rate for the pump with the pressure differential across the pump, (b) detecting data from which the differential pressure across the pump can be computed, (c) utilizing a computing means to accomplish the following at sequential points of time: (i) compute the differential across the pump on the basis of said data, (ii) access said table in the memory means in order to determine the pumping rate corresponding with the computed pressure differential, (iii) calculate the volume pumped during the time interval between the current time point and the immediately preceding time point by multiplying the determined pumping rate by the length of the time interval, and (iv) update a totalizer in the memory means by adding in the calculated volume pumped during the respective interval.