Before submitting any proposition for borrowing money for any of the purposes mentioned in sections 16-673, 16-674, and 16-680, the mayor and city council shall determine upon and adopt a system of sewerage, waterworks, heating, lighting, or power, as the case may be, and shall determine upon and adopt a plan for constructing drains or culverts, or for doing other work upon or in connection with watercourses or waterways as authorized in section 16-680. The mayor and city council shall procure from the city engineer an estimate of the actual cost of such system, an estimate of the cost of so much thereof as the mayor and city council may propose to construct with the amount proposed to be borrowed, and plans of such system. The estimate shall be placed and remain in the hands of the city clerk, subject to public inspection during all the times such proposition to borrow money shall be pending. After a system shall have been adopted, no other system or plan shall be adopted in lieu thereof unless authorized by a vote of the people. After construction of any such systems, works, or improvements as are authorized in sections 16-673, 16-674, and 16-680, the city may by vote of the people issue bonds to construct extensions, additions, or enlargements thereof, but not to exceed one hundred twenty-five thousand dollars in any one year, and the total amount of outstanding bonded indebtedness of any such city for the initial construction of any such systems, works, or improvements and for the construction of extensions, additions, and enlargements thereof shall not exceed the respective aggregate limitations of amount imposed under section 16-680.