It’s not gone forever. However, it may be in a less useful place.
For example, a well draws water from an aquifer, an underground reservoir; which is refilled by rainwater soaking into the ground. But if water is drawn out of the aquifer faster than it is replenished by the rain, eventually the well will run dry.
Even if that water is still on the planet, it’s not available to your well; and so your well has become useless.