The city auditor shall keep the books of the city and exhibit accurate statements of all moneys received and expended, of all property owned by the city and the income derived therefrom, and of all taxes and assessments. In cities having a population of less than twenty thousand the legislative authority thereof may, by a majority vote, merge the duties of the clerk of the water works, clerk of the board of control, and clerk of such legislative authority with the duties of the auditor, allowing him such additional assistants in performing such duties as the legislative authority determines.