Mass. Gen. Laws ch. 40 § 38
A city, by a two thirds vote of its city council, ratified by a majority of the voters thereof at an election called for the purpose, or a town, by action of its selectmen, ratified by a majority of its voters present and voting thereon at a town meeting at which the voting list shall be used, may, for the purpose of supplying water to itself and its inhabitants, purchase of any municipal or other corporation the right to take water from its sources of supply or from its pipes; or may purchase its whole water rights, estates, franchises and privileges, and thereby become entitled to all its rights and privileges and subject to all its duties and liabilities; or, by its board of water commissioners or officers performing like duties, may contract with any such corporation for a supply of water. Any municipal corporation, by its water department, may make such a sale or enter into such a contract to supply water to a city or town.
A city or town having a water supply or water distributing system may develop and use any source of water supply within its limits, not already appropriated for purposes of public water supply, and for such purpose may proceed under any laws applicable to such system as though the authority granted hereby had been contained in such laws; provided, that no source of water supply and no lands necessary for protecting and preserving the purity of the water shall be taken or used without first obtaining the advice and approval of the department of environmental protection.
Nothing in this section shall be construed as authorizing any city, town, or political subdivision which derives any part of its water supply from the Massachusetts Water Resources Authority, except in case of emergency, to use for water in contravention of any provision of the Massachusetts Water Resources Authority Act, and no such city, town, political subdivision nor any water company therein shall purchase water, except in case of emergency, from any municipality without written permission to do so by the said Authority.
Mass. Gen. Laws ch. 40, § 38