Soda does contain water. However, Pepsi, your soda of choice, contains caffeine, which is a diuretic and thus undoes some of the hydration. It also contains phosphoric acid and has a low pH, so it can and does etch and stain your teeth, In addition, if you drink soda instead of juice, you are not getting any vitamins or minerals, just sugar. And finally, Pepsi contains a brown coloring agent. Both that and the caffeine have to be filtered out by your kidneys. Young and healthy kidneys have no problem with that, but if you happen to have weak or susceptible kidneys you can cause permanent kidney damage. And, of course, there are the extra calories from sugar, and the effects on your weight as well as on your pancreas in having to produce enough insulin to keep your blood sugars stable.
You would be wiser in the long run to drink water more often and soda less often.