This means that the cave system functions, hydrologically, as the drainage network for the entire mountain. The rock above, around, and beyond the accessible cave passages is full of water during the rainy season, moving toward the lower sections of the system through routes that no human could follow or map. The volume of water that the cave system must process during a monsoon is vastly larger than what enters through the visible entrance.
For visitors and local people, the cave is safe and accessible during the dry season precisely because all that water has drained away and the passages have dried. The transition from safe to dangerous happens not gradually but in hours: a sufficient rainfall event begins filling the network from multiple entry points simultaneously, and the passages that were walkable in the morning may be chest-deep by afternoon and fully sumped by evening.
This is what happened on June 23, 2018. The team was not caught by a gradual rise of water that they could have retreated before. They were caught by an event that filled the passages faster than a walk back to the entrance could have been completed. The choice was not “exit before the water rises” because there was not time for that choice. The choice was “move to higher ground inside” or be caught in a rising tunnel.
Understanding this explains both the team’s survival through the initial flooding and the difficulty of the rescue. The same hydrology that filled the cave so quickly also maintained the cave full: the mountain was continuously delivering water into the system through routes that no pump could directly address. The pumping teams were fighting not just the water already in the cave but the continuous new water entering from the karst above.