N.H. Rev. Stat. Ann. § 31:137

For the convenient management of any water and/or sewer utility district, a municipality shall vest the construction, management, control, and direction of such district in a board of commissioners to consist of 3, 5, or 7 citizens of each municipality, the commissioners to have such powers and duties as the municipality may prescribe. Their term of office shall be for 3 years and until their successors are elected and qualified. The first board of commissioners may be chosen for terms of one, 2, and 3 years, respectively.