A venturi apparatus comprises: a liquid-receiving section configured to be open to the atmosphere and to receive liquid through an opening at a first end, and having a second end through which the liquid can exit, the second end having a second cross-sectional area that is smaller than a first cross-sectional area of the first end; and a mixing section defining: an intermediate passageway configured to receive the liquid exiting from the liquid-receiving section, the intermediate passageway having a third cross-sectional area that is greater than the second cross-sectional area; and at least one side passageway extending from the intermediate passageway to a perimeter of the venturi apparatus to fluidly connect the intermediate passageway to the atmosphere to allow atmospheric gases to be drawn into the intermediate passageway to mix with the liquid when the liquid flows through the intermediate passageway.