The treasury department will be responsible for the preparation and collection of all utility bills. A system of unified billing shall be utilized whereby charges for electric, water, sewer, pressurized irrigation, drainage and garbage services are combined on one statement ("statement"), and billed on a monthly basis. All owners or occupants of premises in the city shall pay for electric and water services on a metered basis as used, sewer in the same usage as water, and for drainage, garbage and green waste on a flat fee basis, utilizing the person or firm designated for the city to collect appropriate garbage, green waste and rubbish upon such premises. (2015 Code)