A system for reducing an amount of volatile organic compounds which includes: a water-storage tank having a tank containing water, a roof positioned over the tank, and a headspace region formed between the roof and a surface of the water contained in the tank; an air exchange system positioned at least partially in the headspace region that is configured to exchange air exterior to the tank with air inside the tank; and a water conveyance device located at least partially in the water of the water-storage tank and which is configured to convey water in a manner that produces a surface flow velocity. A method reducing an amount of volatile organic compounds is also included.