I think the problem with that idea is....take for instance a liter bottle of soda...with the lid tightly secured, the soda still has its carbonated taste....however if you leave the lid off for even a day the soda gets flat(CO2 is gone)....with your idea, you would have to keep the container storing the soda water air tight...A pump will not be able to work sucking liquid from a sealed container...It would create a vacuum...( I think I,m right about this...not 100% sure)
Thats exactly correct, you would need the soda water air tight, but there would have to be an opening somewhere for the pump to work, otherwise theres a vacuum, if there was an opening it would go flat...
I have a different idea, one tube leading out of the soda water container near the bottom, and have that tube going straight up [so that the water in the container and in that tube both are at the same level]. Then have a tube at the top not dipped in the soda water at all, the soda water container would have to be completely sealed [the smallest hole and it really wouldn't work well, and if it did you would be losing a lot of efficiency], and them pump would work by pressurizing air from the top tube, which would push the soda water up the tube that comes out the bottom. I would think because you are constantly pressurizing the container, it shouldn't go flat, at least not as quickly. What I mean by pressurizing the air through the top tube is doing something like blowing down it, except you would need a mechanism to do it. Haha just thought I would share this modified idea.