The taxes for fiscal year 1978-79 imposed by this chapter shall become operative as of July 1, 1978; provided, however, that the utility companies shall compute and impose the utility users’ tax upon said users for the charges set forth in this chapter at the commencement of the billing period for said users arising from and after July 1, 1978 for services provided to said users in accordance with accepted billing practices of said utility companies, so that there will be no need to prorate said utility users’ tax. The tax imposed for fiscal years 1979-80 and beyond shall be operative as of July 1, 1979. (Ord. 1803 § 1, 1978; Ord. 1288 § 2, 1970).