Diet soda may taste nice and fuzzy while having nearly the same calories as a glass of water, but underneath that surface view the contents of soda are more like a chemists science lab, than the great flowing rivers of and valleys full of fresh spring water.
Many diet sodas contain a chemical called aspartame, which is also used in certain pesticides. While in the small does it's probably not killing you and maybe not even doing any harm at all, it's still not something I would feel safe drinking regularly. Also, regular soda can sometimes be scary. Certain soda's can even take the paint off a car when left out for long periods of time. If thats what it does to your car, what is it doing in your stomach?
Now perhaps you are one of those regular soda drinkers going for a break and want to lose a few pounds. I personally would recommend water as natures drink for all occasions, but if you like a little flavor you can throw a lemon slice in it. Also unsweetened ice tea is pretty healthy too.
I personally like to stick with natural juices and water, especially in the morning. Then I drink green tea when i feel i need a little pep. In the morning I go with a little orange juice with calcium to help fight off sickness. It is your life though, I cant tell you how to live. Drink what you want just know the facts. So next time think about what you are drinking and not in diet soda start sinking.
You are right about the water though.