All materials, supplies and services shall be specified upon a written requisition therefor by the officer, board or department head requiring the same. Requisitions shall be supplied, insofar as possible, out of the general stores of the City. If not available therefrom, purchases shall be made after bids are received, when required by the City Charter, by ordinance or by direction of Council. When the securing of bids is not required, purchases shall be made in the open market to the best advantage of the City.
(1979 Code Sec. 3.16.020)