Edgar hit the jackpot. The clu here is drink caffeinated drinks in moderation. Caffeine does have a diuretic effect but that effect and its duration is doses dependent. The more you consume the more effect it will have. Caffeine in high doses causes hypertension and promotes sodium retention.
This kind of problems occur in people who drink energy drinks, those nasty beverages have more caffeine that your normeal coffee or coke.
So, no, caffeine alone will not dehydrate you if you consume it with moderation. Just be sure to consume also enough pure water between meals.