A Reiquarium is a self-contained body of water containing Rei Ayanami and/or her clone(s), a character from the anime Neon Genesis
Evangelion -- be it a hot tub, tank (see episode 23),
swimming pool, pond, lake, sea, ocean, or
water world.
Lengths of running water such as brooks, creeks, streams, and rivers containing Rei Ayanami and/or her clone(s) ARE NOT Reiquariums because they are fed from and empty into self-contained bodies of water (see above).
Misato took
the three Children and Pen Pen on a vacation trip to Okinawa. While Misato, Shinji, and Pen Pen had fun
on the beach, Rei and Asuka went
SCUBA diving -- thus turning the East China Sea into a Reiquarium.
