Section 21.06 - Collection By End Suppliers(1) Amounts payable as Assessments and administrative costs o f end suppliers related to the Assessment shall be recovered to the maximum practical extent from charges to users. End suppliers may recover from users administrative costs relating to the Assessment, in an amount not to exceed 5% of the annual Assessment for that system. Interest on overdue remittances, including applicable penalties, shall be borne by the end suppliers.(2) To the maximum extent practicable, the Assessment shall be apportioned among users by end suppliers based on the number of gallons of water consumed, or the estimated number of gallons consumed by each user.(3) Each end supplier shall have the option of determining how its invoices to users shall show such defraying amounts and shall determine the frequency of invoicing.(4)310 CMR 21.06(4) shall not apply to the manner in which investor owned end suppliers apportion and collect the Assessment from users, which shall be determined by the Department of Public Utilities in accordance with 310 CMR 21.08.