The board shall annually levy a tax upon the taxable property in the district sufficient to pay the interest on bonds for the year, and such portion of the principal as is due or is to become due during the year, so that the entire amount of principal and interest of the bonds shall be paid at or before maturity, and in any event within forty years of the date of issuance of the bonds.
(Enacted by Stats. 1939, Ch. 60.)