Md. Code, Environment § 5-408

(a) The Authority shall assess and collect charges for payment of the State’s share of the initial cost of the project. Each represented county is assessed at a rate calculated from a cost-sharing formula based on a withdrawal ratio calculated as the sum of the average daily withdrawals from the Potomac River by all represented counties and non-Maryland users during the month of maximum withdrawal in the preceding calendar year divided into the average daily withdrawals for the county from the Potomac River during the same month.

(b) The Authority shall assess non-Maryland users subject to appropriation requirements in § 5-502 of this title based on a rate calculated by the same means used for assessment of represented counties. The Authority shall collect assessed charges from non-Maryland users in a manner the Authority prescribes.

(c) The Authority may enter into any contract or agreement with the government of the District of Columbia for the District of Columbia to pay the Authority its equitable share of initial cost of the project. The contract shall contain provisions to which the Authority and the government of the District of Columbia agree and may include provisions to ascertain the District of Columbia’s equitable share of costs, periodic revision of the amount of that share, and other cost payments by the District of Columbia. Any executed contract or agreement has full force and effect as a contract between the District of Columbia and the State.

(d) An assessment of charges shall be:

(1) Determined when the first payment is due, based on the preceding calendar year’s daily withdrawal information; and

(2) Updated annually.