Any part of the proceeds of the sale of an obligation issued under this chapter that are unspent after the project for which the obligations were authorized is completed may be paid into the sinking fund for the payment of the obligation and may be used only for:

1. (1) the payment of the principal of the obligation; or
2. (2) the purpose of acquiring outstanding obligations by purchase in the manner provided by this chapter.

Acts 2003, 78th Leg., ch. 1277, Sec. 1, eff. April 1, 2005.