Some people say that thirsty is the sign of dehydration. But in the fact, thirsty is not the same as dehydration. Thirsty is the body sign to tell us that our body lack of fluid. If there is no action of this condition, it can cause dehydration of our body.
Fluid is not just water. Consuming tea, coffee, and the other drink can be source of fluid for our body. But water is better because there is no sugar on it.