A county may pay for relocating a water line owned by a water control and improvement district if:
(1) the relocation is necessary to complete construction or improvement of a farm-to-market road as described by Section 256.008; and
(2) the district agrees to pay the county for the relocation costs:
(A) within 20 years; and
(B) with interest at a rate equal to the rate paid by the county on its road and bridge fund time warrants.