When, in the opinion of the board of a municipal improvement district or the boards of different improvement districts, where combined and acting together in a city or town, it shall be necessary for the benefit of the inhabitants residing in the district or districts, it shall be lawful for money raised by assessment in the districts to be expended in:
(1) The purchase of lands or erection of houses, reservoirs, or other improvements necessary for the proper construction and operation of waterworks outside of the limits of the city or town in which the districts exist;
(2) The construction and operation of any portion of a sewerage system, or acquisition of rights-of-way therefor, which may be extended outside of the limits of any such city, town, or improvement district.