(Q) Principle:

If a barrel of water (which is considered drawn) fell into the Mediterranean sea, and a person (or a terumah  food) immersed in that spot, he is still considered  impure, even though the drawn water fell into a “completed” Mikveh, thereby, nullifying it.

 

(A) In order to keep the people far away from using drawn water to fill a mikveh, the Rabbi’s decreed that if three lugin of drawn water came on a person’s head and most of his body (shower) on the same day as his immersion, he will become impure again. People started to confuse the shower with the mikveh. Being that the waters of the Mediterranean (or the like) are “stationary”, the Rabbi’s extended the decree to this case. We consider an immersion that followed a barrel of water falling in, to be as though one had at least three lugin of drawn water come on him. This decree was on stationary water, not moving water. 

 

 

      *Connection: Same author (Rav Yehudah) and topic as previous sugya*