N.Y. Gen. Mun. Law § 120
The local authorities of the several counties, cities, towns and villages of the state having charge of the supply of water and the care of sewerage in their respective localities, are hereby authorized, on behalf of their counties, cities, towns and villages, respectively, to enter into contracts with the owners of any process or apparatus for the purification of water and sewerage whether protected by patents or not, and either contract for the use of apparatus and process for a term of years or for the purchase of the same, as to them shall seem advisable. It shall be lawful for any two or more of such municipalities in this state, without regard to the form of their incorporation, including towns or sewer districts of towns, to jointly construct, provide, maintain and operate a comprehensive system of sewerage including trunk lines and laterals, or a system of conveying or conducting sewerage from said municipalities from a point or points to be agreed upon to a common destination or disposal plant or plants, and to construct, maintain and operate within or without the said municipalities or any of them one or more outlet or trunk sewers, plants, works or stations for the treatment, disposal, or rendering of sewerage, or any such municipality or any such municipalities may jointly or severally contract for the construction for it or them of any such system, extension or part thereof, including any such sewers, plants, works or stations, and agree to pay annually, semi-annually or quarterly for the use or possession thereof, by way of permanent rental reserved therefor; or such lawful authorities of the respective municipalities may jointly or severally contract with any person, persons or corporation or with other municipalities or sewage districts for the removal of sewage within the boundaries of such local government, upon such reasonable terms as they may agree upon. And to that end the governing bodies or boards of any two or more municipalities, including sewer districts of a town, authorized by law to have charge of sewer systems established or to be established in said municipalities, or sewer districts of a town, respectively, may unite and jointly cause to be made at their joint expense (each district bearing a part of the expense in proportion to the assessed valuation of real estate in such district, or on such other basis or division as may be jointly agreed upon) by competent engineers, mechanics and others, surveys, maps, plans, reports and estimates of proposed works and improvements relating to such contemplated public improvement or works authorized by this act, which such municipalities may desire to jointly provide, maintain, operate or lease under the authority conferred by this act, and for such purpose they may determine upon the final route and plan for the building or construction of such sewerage system and for the making of such surveys, maps, plans, reports and estimates as provided in this section. It shall be lawful for the officers and agents of such municipalities to enter at all times upon any lands or waters for the purpose of exploring, surveying, and laying out the route of such sewerage system.
N.Y. Gen. Mun. Law § 120