Wis. Stat. § 198.167
The directors of the district shall employ annually the commission or a certified public accountant licensed or certified under ch. 442 approved by said commission who shall be qualified to, and who shall with all due diligence, examine and report upon the system of accounts kept by the district, all the contracts of whatsoever kind made and entered into by the board of directors within the year immediately preceding, and the properties and investments of the district. The certified public accountant shall in the report make such recommendations and suggestions as to the certified public accountant shall seem proper and required for the good of the district, and the efficient and economical or advantageous management and operation of the public utility or utilities of the district; and the certified public accountant shall in the report make such recommendations and suggestions as to the system of accounts kept, or in the certified public accountant's judgment to be kept, by the district, in connection with each public utility, the classification of the public utilities of the district and the establishment of a system of accounts for each class, the manner in which such accounts shall be kept, the form of accounts, records, and memoranda kept or to be kept, including accounts, records, and memoranda of receipts and expenditures of money, and depreciation and sinking fund accounts, as in the certified public accountant's judgment may be proper and necessary, and shall not conflict with the requirements of the commission.
Wis. Stat. § 198.167