The directors may borrow money, not exceeding in amount the assessments or annual installments unpaid at the time of borrowing, for the construction of any work which they may be authorized to construct, or for the payment of any indebtedness that they may have lawfully incurred under the provisions of sections 245.285 to 245.545, and may secure the same by notes or bonds bearing interest at not exceeding eight percent per annum, and not running longer than one year beyond the date of the payment of the assessment, or the last annual installment thereof, on account of which the money is borrowed; which notes or bonds shall not be held to make the directors personally liable for the money borrowed, but shall constitute a lien upon the assessments, or annual installments thereof, for the repayment of the principal and interest of said notes and bonds.