Sec. 561.1. Classification of utilities

(a) For the purpose of applying systems of accounts prescribed by the commission, water utilities are divided into four classes, as follows:

Class A. Utilities having annual water operating revenues of $1,000,000 or more.

Class B. Utilities having annual water operating revenues of $700,000 or more but less than $1,000,000.

Class C. Utilities having annual water operating revenues of $400,000 or more but less than $700,000.

Class D. Utilities having annual water operating revenues of $100,000 or more but less than $400,000.

(b) This system of accounts applies to Class A and B utilities. Those applicable to Class C and Class D utilities are issued separately.

(c) The class to which any utility belongs shall originally be determined by the average of its annual water operating revenues for the last three consecutive years. Subsequent changes in classification shall be made when the annual water operating revenues for each of the three immediately preceding years shall exceed the upper limit, or be less than the lower limit, of the annual water operating revenues of the classification previously applicable to the utility.

(d) Any utility may, at its option, adopt the system of accounts prescribed by the commission for any larger class of utilities. Notice of such action shall be promptly filed with the commission.