(1)    The property taxable under s. 76.13 shall include all franchises, and all real and personal property of the company used or employed in the operation of its business, excluding property that is exempt from the property tax under s. 70.11 (39) and (39m), such motor vehicles as are exempt under s. 70.112 (5) and treatment plant and pollution abatement equipment exempt under s. 70.11 (21). The taxable property shall include all title and interest of the company referred to in such property as owner, lessee or otherwise, and in case any portion of the property is jointly used by 2 or more companies, the unit assessment shall include and cover a proportionate share of that portion of the property jointly used so that the assessments of the property of all companies having any rights, title or interest of any kind or nature whatsoever in any such property jointly used shall, in the aggregate, include only one total full value of such property.

   (2)   If the property of any company defined in s. 76.28 (1), except a qualified wholesale electric company as defined in s. 76.28 (1) (gm), is located entirely within a single town, village or city, it shall be subject to local assessment and taxation.

   (3)   Any air carrier company engaged solely in intrastate transportation and using the facilities of only one airport within this state is exempt from taxation under this subchapter and is subject to local assessment and taxation.

   (4)   Nothing in this subchapter shall be construed to result in the levy, assessment or collection of taxes on property of a municipal water utility created under s. 198.22.