A system and method for carbonizing a liquid, such as tap water with CO.sub.2, are disclosed. The liquid is carbonized inside a pump housing, thereby obviating the need for a separate high-pressure carbonator tank and a separate feed pump. The pump housing has an inlet for receiving in combination the liquid and CO.sub.2 at a first pressure, and an outlet for transporting the liquid carbonized with CO.sub.2 from the pump housing into an outlet line at a second pressure higher than the first pressure. A constriction is disposed in the outlet line for producing said higher pressure with the pump. The system and method can be employed in closed-loop carbonizing systems in the beverage industry.