The head of each agency shall establish the procedure by which charges and liabilities may be incurred on behalf of the agency. Such procedures shall ensure that no officer or employee, on behalf of or in the name of the agency, shall incur a liability or an expense for any purpose in excess of the amount appropriated or otherwise authorized therefor; and no charge, claim or liability shall exist or arise against the city, or any of the counties contained within its territorial limits, for any sum in excess of the amount appropriated or otherwise authorized for the particular purpose.