The board of supervisors of any county may adopt a model county sanitation district ordinance. The procedure for the adoption of said ordinance shall be the same as is provided for in Article 7 (commencing with Section 25120) of Chapter 1, Part 2, Division 2, Title 3 of the Government Code for the adoption of county ordinances. The ordinance may be amended by the same procedure used for the adoption of the ordinance. The ordinance and amendments thereto shall be effective only as to districts which have adopted it by reference as hereinafter provided.