The Superintendent shall make a test of the accuracy of any water meter at any time when requested in writing. If it is found that such meter overruns, the cost of the test shall be paid by the City and a refund shall be made to the customer for the estimated overcharges collected since the last known date of accuracy, but not for a longer period than 3 months. If the meter is found to be accurate or slow, the user shall pay a testing charge of $25.00.