Nothing herein contained shall prohibit the mayor and city council from amending, altering, or adding to the provisions of this chapter in relation to the water supply or the rules of same which may be adopted in conformity therewith; provided, that no alteration in water rates shall apply to any charge upon, or contract made with, an owner under this chapter until after the expiration of the time for which such charge was made or contract entered into. Hereafter when, and/or if, the mayor and city council deem it advisable to alter the water or installation rates or charges as in this chapter recorded, such changes shall be made by resolution. (2003 Code § 9-01-23)