There's decaf tea, like there's decaf coffee, but it's still camellia sinensis.
Now, if you're talking about herbal tea, there are a bajillion different kinds: rooibos, chamomile, lavender, etc. Some herbal teas do have caffeine (such as yerba mate), but most do not.
This is largely a myth. While it's true that caffeine is a diuretic, the effect on hydration is very small. This is especially true for tea, which has minimal amounts of caffeine. Hospitals are not full of people who got dehydrated from drinking too much coffee or even energy drinks.
Do a web search for "caffeine dehydration myth" (no quotes). There are lots of articles on the topic.
As long as you drink water when your body wants water you'll be good. It doesn't matter how much you urinate. Your body know how to take care of itself. Just listen to it.
