On establishing a stormwater management district, Montgomery County and Prince George’s County each shall: establish a stormwater management fund; and deposit in the fund: receipts and revenues from an ad valorem tax imposed under § 21–623 of this subtitle; and charges, fees, fees–in–lieu, and other contributions received from any person or governmental unit in connection with stormwater management activities or practices. Money in a county stormwater management fund shall be used only to pay for the costs of stormwater management as set forth in § 21–623(a) of this subtitle.