Feivel-
3) A mikva holding precisely forty se’ah of water, and a person who requires tevila. After the tevila, the person is tahor, but the mikva is no longer kosher, and won’t be until enough water is added to bring it back to forty se’ah.
Moderator – I posted this earlier, but it may have gotten lost. Please don’t double-post this if you just haven’t posted what I sent about an hour ago.