If any person fails to pay annual charges within the periods specified in § 11.20, a penalty of 5 percent of the total delinquent amount will be assessed and added to the total charges for the first month or part of month in which payment is delinquent. An additional penalty of 3 percent for each full month thereafter will be assessed until the charges and penalties are satisfied in accordance with law. The Commission may, by order, waive any penalty imposed by this subsection, for good cause shown.