After a water system has been constructed or upgraded pursuant to the provisions of Sections 21-25-51 through 21-25-59, the municipality which reimbursed or paid a rural water system for the cost of such construction or upgrading shall not be charged with the costs of such construction or upgrade upon its purchase of the water system. The price of such newly constructed or upgraded water system shall be reduced by an amount equal to the costs paid by the municipality to the rural water system for such construction or upgrading of the water system.