For service calls made by a customer to the City relating to the water system, there shall be a charge of as set by resolution of the City Council to the customer for time spent by City employees after normal business hours (including, but not limited to, all hours spent during the weekends or holidays). The charge shall only be imposed if the service call relates to that portion of the water system which the customer is responsible for under 90.11 of this Code of Ordinances. The charges shall commence at that time that it was first determined that the service call in fact related to that portion of the water system which the customer is responsible for.