Refunding bonds of any maturity may be used at face value in paying assessments levied to pay the principal of refunding bonds, if bonds so used have all future due coupons thereto attached and no credit shall be allowed for such coupons. Interest coupons maturing in any year may be used at face value in paying interest assessments which become due and payable in that year.
C.R.S. § 37-26-115