It shall be lawful for the Council of the Borough of Wanganui, for the purpose of constructing the works aforesaid, to impose and levy special rates to defray all costs interest charges and expenses connected with the supply of gas water and drainage, or either of them, and the said rates shall be made and levied and be paid in the same manner as the other rates are made and levied by the said Council, and paid under the authority of any Act or Ordinance now in force: Provided always that private consumers of water and gas, or either of them, shall be charged for the quantity of water and gas, or either of them, used or consumed by them respectively at such rates as may be from time to time fixed by the said Council, over and above any special rate which may be payable for water and gas, or either of them, consumed for public purposes, or connected with the supply of water and gas.