Iowa Code § 428.24: Public utility plants.

The lands, buildings, machinery, and mains belonging to individuals or corporations operating waterworks, other than waterworks taxed under chapter 437B, or gasworks or pipelines, except those natural gas pipelines permitted pursuant to chapter 479, shall be listed and assessed by the department of revenue. In the making of assessments of waterworks plants, the value of any interest in the property assessed, of the municipal corporation where it is situated, shall be deducted, whether the interest is evidenced by stock, bonds, contracts, or otherwise.