The assessment levied under this chapter shall become due and payable, and shall be delinquent at the same time as state and county taxes become due and delinquent. On November 15 after such assessments become delinquent, a penalty of ten percent (10%) of the amount of such assessments shall accrue on the delinquency, and in addition such assessments shall bear interest at the legal rate from the date they are delinquent until paid, to pay the cost of collecting them so as to hold the district harmless.