The green liquid in the basin

[grouchymedic_26149]

No: HPFGUIDX 165644

Hello, all,

Paul From WV. here. One thing puzzles me, and I apologize in advance if 
it has already been discussed. Reference HBP, when Harry and DD travel 
to the cave on the seashore to retrieve the horcrux. I am curious about 
the green liquid in the basin in the middle of the lake that contained 
the horcrux. How did the basin get refilled? If the basin had been 
emptied before, by who ever took the horcrux, it should have still been 
empty. Is the basin enchanted, so that it refills it's self when 
emptied? If not, who refilled it? Food for thought.