If you were stranded in the Desert, and the only thing to drink was a Pespi (Or Coke Whatever). Would you be better off drinking it or not drinking it? Would you become more hydrated by drinking the soda or by just letting yourself be?
soda has water in it.. so it would be better than nothing. Soda does not dehydrate you, it's simply not the best option for hydration since it contains caffeine and sodium.