N.H. Rev. Stat. Ann. § 38:30

Any municipality or municipal water company supplying water to the public for domestic use shall have the power to take by the exercise of the right of eminent domain any property needed to protect the purity of the water so supplied, upon petition to the superior court or in the case of a village district to the board of selectmen of the town or towns within which the district is situated and proceedings thereon as in case of a petition for the laying out of a highway.