The accounting system for the water and sanitary wastewater utilities:shall conform to generally accepted principles of utility accounting; and shall be kept on the accrual basis and in the manner prescribed in <cite data-doc="City of Baltimore, Md., Charter" data-path="VII|§11">Article VII, § 11 of the City Charter</cite>. The records of revenues of each said utility shall be kept so that the sales made to each class of customer according to the rate schedules adopted by the Board of Estimates for each utility can be determined. City Code, 1976/83, art. 29, §21A(a)(1st, 2nd sens.) Ord. 78-941