Section 4. In any city or town which accepts the provisions of this chapter, there is hereby created a body politic and corporate and political subdivision of the commonwealth to be known as the water and sewer commission of the municipality. The commission is hereby constituted an independent public instrumentality and the exercise by the commission of the powers conferred by this chapter shall be deemed and held to be the performance of an essential public function. The commission shall not be subject to the supervision of the municipality or of any department, commission, board, bureau or agency of the municipality except to the extent and in the manner provided in this chapter.

Except as otherwise provided in this chapter, the powers of the commission shall be exercised by a board of three members, each of whom shall be a resident of the municipality. These members shall be appointed by the local appointing authority in accordance with the municipal charter. The members shall include one member with extensive experience in the field of administration or business, and one member with extensive experience in the field of finance or accounting. Of the members first appointed, one shall serve in office for a term expiring on June thirtieth in the year following the acceptance of this chapter, and one for a term expiring on June thirtieth, in the second year following the acceptance of this chapter and one for a term expiring on June thirtieth, in the third year following the acceptance of this chapter. Thereafter, the local appointing authority shall appoint successors for a term of three years or, in the case of an appointment to fill a vacancy, for the unexpired term, and until his successor is appointed and qualified. Any member of the commission shall be eligible for reappointment. Any member of the commission may be removed at any time for cause in accordance with the removal procedures then in effect in the municipality. No vacancy in the membership of the commission shall impair the right of a quorum to exercise the powers of the commission. Two members of the commission shall constitute a quorum and the affirmative vote of two members shall be necessary for any action taken by vote of the commission. Any such action shall take effect immediately unless otherwise provided and need not be published or posted.

The commission shall annually elect one of its members as chair. The commission may establish, with the approval of the local appointing authority a reasonable per diem compensation for its members for attendance upon the business of the commission. Such amount may be payable to each member for one day in each month and for any additional days as may be approved by the local appointing authority. In addition, each member may be reimbursed for all reasonable and necessary expenses incurred in the discharge of official duties as approved by the commission. In accordance with chapter two hundred and sixty-eight A, the commission shall be deemed to be a municipal agency and the members of the commission shall be deemed to be special municipal employees.

The provisions of sections twenty-three A to twenty-three C, inclusive, of chapter thirty-nine shall apply to all meetings of the commission and section ten of chapter sixty-six relating to the availability of public records as defined in clause twenty-sixth of section seven of chapter four shall apply to the commission.

The commission shall be deemed to be a public employer within the meaning of chapter two hundred and fifty-eight. The members, officers and employees of the commission shall be deemed to be public employees within the meaning of chapter two hundred and fifty-eight. The commission shall be liable in tort for defects in a public way to the same extent as the municipality under chapter eighty-four.

The commission and its employees shall be subject to the provisions of chapter one hundred and fifty E, to the extent said provisions are applicable, and for purposes of said chapter, the commission shall be considered an ''employer'' or ''public employer'' as defined therein. The commission may designate a representative to act in its interest in dealing with employees of the commission and the term ''legislative body'' as used in chapter one hundred and fifty E shall mean the commission.

The commission shall be deemed a district for purposes of chapter thirty-two B. The commission and the municipality may enter into such arrangements as they deem suitable for provision of insurance benefits jointly for employees of the commission and employees of the municipality under said chapter thirty-two B.

The commission may be self-insured for the purpose of workers' compensation under chapter one hundred and fifty-two.