Soda is really bad! I cant stand it! I have been trying to have more water because I just got rid of a kidney stone. I bought a glass container on ebay and I have been cutting up lemon slices. I put the water in the glass container, add the lemon slices, add a couple mint sprigs, and a pinch of dried lavender. Put in the fridge for about 30 mins to an hour. The water tastes amazing, I am so addicted! I think you just need to come to terms that soda isn't worth it. It is bad for you in every way. It doesn't nothing to quench thirst. It actually makes you more thirsty. If you are focusing on soda, you are less focusing on water which is vital to the lungs. Also we are prone to kindney stones, thrust me, you don't want one of those! Natural is the way to go, give you body what it needs to help with the CF instead of hurting it.