Unless otherwise approved by the Commission, each service water meter shall be periodically inspected and tested in accordance with the following schedule, or as often as the results may warrant, to insure that the meter accuracy is maintained within the limits set out in Section 600.310:

⅝ inch meter – 10 years or for each 100,000 cubic feet registered

¾ inch meter – 6 years or for each 300,000 cubic feet registered

1 inch meter – 6 years or for each 300,000 cubic feet registered

Meter 1½ inch and over – 4 years