Terror in the Pool (Terror en la Piscina)

On a late-night call, caretaker Mara arrives at the abandoned municipal pool. The exit seals behind her and something knocks from the drain. Activate the valves, drain the pool and escape the monster. There are seven nights in a row, and each night adds one more valve: from 3 up to 9. If it closes in, flash your light to stun it for a moment and make a run for it.