For the more convenient management of local operations, any municipality which has a municipal, gas, electric, or waterworks system under RSA 38, a municipal sewer system under RSA 149-I, or highway agents under RSA 231:62 or any combination, may combine any 2 or more of the following into one board of public works commissioners:
I. Board of sewer commissioners.
II. Board of commissioners of a gas, electric, or waterworks system.
III. Highway agents.