Flat soda may indicate that you have not carbonated properly. After twisting the carbonating bottle into place, press the carbonating button ALL THE WAY DOWN in firm short bursts. You will hear a hissing sound at first. Continue to press the button in firm short bursts until you hear a LOUD BUZZ. The loud buzz indicates the first level of carbonation. Three loud buzzes will achieve average carbonation.
Another tip: Make sure you use very cold water for carbonation. Cold water (from the refrigerator) holds carbonation much better than cold water from the tap. We recommend keeping carbonating bottles full of water in your refrigerator so they are always ready to go when you want a fresh soda!