I LOVE getting roses, but they never lasted very long and I always felt bad that they would be dead in a week or less. Not with soda! Don't worry about adding any extra water, just trim the bottom of the stems and place them in the vase full of soda. Within about twenty minutes you will see that many of the flowers are opening up! I had one bouquet of roses that lasted so long the sugar crystalized on the rose petals, making them sparkle. It was awesome!
Right now I have a wild flower type bouquet with carnations, daisies, snap dragons, lilies, a big purple flower and little white flowers. There were only a couple lilies that were slightly opened. The soda has encouraged them all to open up, and the bouquet looks gorgeous and it's been on my counter top for more than a week! At this point, when we buy flowers, we also buy a bottle of soda, even if I'm giving them away. It makes me feel better knowing that the flowers I give are going to last a good long time!