Sec. 51.437.  INVESTMENT OF SINKING FUND.  (a)  The board may invest any portion of the sinking fund of the district in bonds of the United States, the state, any county or city in the state, any irrigation or water improvement district, school district, or other tax bonds issued under the laws of the state.
(b)  The funds may be invested if the bonds to be paid with them do not mature within three years from the time the investment is made and if it is necessary to preserve the best interest of the district.
Acts 1971, 62nd Leg., p. 343, ch. 58, Sec. 1, eff. Aug. 30, 1971.