In addition to all other powers and authorities of any irrigation district now or hereafter organized under the laws of the state of Idaho, such irrigation district may, in connection with any contract with the United States under the Federal Reclamation Law (being the act of June 17, 1902 (32 Stat. 388) and acts amendatory thereof or supplemental thereto) for the construction, operation or maintenance of a domestic water system, together with an irrigation system, provide for the apportionment of benefits and make charges for either or both, including the levy of an annual assessment, on any bases permitted or required by the Federal Reclamation Law and by such contract, including, without limitation by reason of this enumeration, a plan in the case of a district embracing substantial areas devoted to suburban residences, under which such district is required to establish total annual assessments and charges against benefited lands for both construction payments and operation and maintenance costs, which are to be proportional, as nearly as practicable, to the relative repayment ability of the various sized operating units in single ownership, to which irrigation service is provided.