At the time of making the general tax levy after incurring the bonded indebtedness, and annually thereafter until the bonds are paid or until there is a sum in the treasury set apart for that purpose sufficient to meet all payments of principal and interest on the bonds as they become due, the legislative body shall levy and collect a tax sufficient to pay the interest on the bonds and such part of the principal as will become due before the proceeds of a tax levied at the next general tax levy will be available.