What effect does low CO2 supply have on drinks from the soda machine?

Low CO2 supply affects drinks from the soda machine by resulting in a flat taste. Carbon dioxide is responsible for carbonation in beverages, which provides that characteristic fizziness and tangy flavor. When the CO2 supply is low, the drinks lack the necessary carbonation that contributes to their taste profile. This results in a lack of effervescence, making the drinks feel less invigorating and more dull, which is typically described as "flat."

While low CO2 can also make drinks seem less fizzy, the more salient and noticeable effect is the flatness in taste, as the absence of carbonation leads to a significant change in how the beverage is perceived by the palate. Therefore, the statement accurately reflects the primary impact that low CO2 levels have on the drinking experience from the soda machine.