Do cola drinks really make one thirty thirsty?

What about other drinks, like 7-Up? Tea? This is a serious question, actually, because my doctor said I need to cut back on my water and liquid intake due to a low sodium count. I used to drink a LOT of water because I thought it was good for you, but I guess not. I certainly don’t want to drink something that’s going to make me thirsty, but I do love my Diet Coke. If I need to, though, I’ll give it up.

Along with the main question, any other suggestions are welcome.