The body adapts to consistent caffeine levels. I ingest a bare minimum of 400mg caffeine a day and only encounter dehydration when I wake up in the morning, which has nothing to do with caffeine and everything to do with not drinking anything for 8 hours straight.

The bottom line is that if you're peeing a color, you need another glass of water. Incidentally, thirst is also often mistaken for hunger, so drinking is a great way to avoid unplanned snacking.