If at any time a water meter shall fail to register the quantity of water used or flowing through the same, the quantity used or flowing through such meter shall be determined by making an average of the four readings last preceding the discovery of the defect in such water meter and a charge shall be made for the period during which such water meter failed to register or during which such defect existed based upon such average unless it shall be made to appear by evidence satisfactory to the superintendent of water that the conditions during such period were materially different from those which existed during the period covered by the last preceding four readings. In case it shall appear that the conditions were such during the period of such failure or defect that a change in conditions had taken place or that a lesser amount of water was used during such period on account of changed conditions, the superintendent of water shall make a charge for the water used during such period based upon the amount of water estimated to be used during such period, as shown by the evidence submitted to him or her.
(1929 Code, § 797)