Systems, methods and cartridges for carbonating or otherwise dissolving gas in a precursor liquid, such as water, to form a beverage. Carbonating gas can be provided to a tank via the tank outlet, thereby purging at least a portion of a dispense line leading from the tank to a dispensing station. A single pump may be used to deliver liquid to the tank, e.g., for carbonation, and to pump pressurized air to dispense liquid from the tank. A water trap may help remove moisture from carbonating gas.