Idaho Code § 42-4219
Assessments shall be due and payable on or before December 31 of each year. On or before the first day of December, the treasurer of the district shall publish a notice for a period of not less than two (2) weeks in a newspaper published or having general circulation in each of the counties in which any part of the district is situated setting forth the date by which assessments must be paid and the times and places at which payment may be made.
Assessments unpaid on December 31 shall be delinquent and shall bear interest at the rate of eight percent (8%) per annum until paid. Delinquent assessments, in addition, shall be subject to a penalty in the amount of fifty cents ($.50) per second foot of water the water user is entitled to appropriate under the water right or rights forming the basis of his assessment.
The maximum annual assessment limitation specified in section 42-4215, Idaho Code, shall apply only to the amount of the assessment itself, and the interest and penalty herein prescribed shall be collectible along with the amount of the delinquent assessment, notwithstanding that the assessment itself is at the maximum specified in that section.
Idaho Code § 42-4219