The said commissioners shall prepare plans and specifications of all work to be performed and materials necessary for the repair, maintenance, and extension of such water-works, or the erection of new water-works; and shall, after plans and specifications for the extension of water-works or the erection of new water-works have been submitted to and approved by the Department of Health, in accordance with the provisions of an act of Assembly, approved the twenty-second day of April, one thousand nine hundred and five, entitled “An act to preserve the purity of the waters of the State, for the protection of the public health,”¹ and a permit granted therefor by the Commissioner of Health,--by due public notice, invite proposals for the performing of such work and the furnishing of such materials; and shall, in all cases, let the contracts therefor to the lowest responsible bidder, and shall take adequate security for the performance of such contracts.