In the event that the Director of Water Distribution and Accounting or his agent shall be satisfied that a portion of the water consumed upon any premise is not accurately reflected by the main service meter, then the owner and/or other interested party may at their expense, install and maintain such separate metering devices as shall demonstrate to the satisfaction of said Director, what portion of this metered water is actually discharged to the sanitary sewer. Such portion shall be the basis for measuring the flows and loads under this provision. Each meter shall constitute a separate service for billing purposes.