Question: Does the water in the mikva used for tevila need to be constantly connected to the bor hashoko, or does it suffice if the two bodies of water are connected once?
Answer:
First of all, a mikva needs to contain 40 se’ah (approx. 1000 litres or 1 cubic meter) to be kosher, if the mikva contains less than this, the tevila is invalid.
Many mikvaos are connected to a bor hashokoh. (The term “mikva” here refers to a bor tevila – i.e., water that is actually used for tevila. A bor hashokoh is a collection of 40 se’ah of rainwater connected to the bor tevila, that enables the bor tevila to be cleaned and the water changed without affecting the kashrus of the mikva).
The bor tevila is usually connected to the bor hashokoh through a connecting channel in the mikva wall (often circular). This channel (called the nekev hashokoh) is generally located slightly under the water line. The diameter of this channel (as well as the water within) must be the width of two fingers (approx. 5-6cm) . If the water level drops and the connecting channel is therefore no longer completely full of water, there are two serious problems:
Firstly, if the water level in the bor tevila is lower than the nekev hashokoh, the bor tevila is disconnected from the bor hashokoh and therefore may not be kosher for tevila (see footnote ).
Secondly, if the connecting channel is only partially full of water (instead of completely full of water) the mikva may now be considered zochalin (“moving”) and may not be used for tevila . The reason for this is because one of the essential properties of a mikva is that it must be stationary.
Let us elaborate on this point:
When the water level is higher than the nekev hashoko (and therefore the nekev hashoko is completely full of water) a connection has been created between the bor tevila and bor hashoko, and these two boros are now viewed as one halachic entity. Just as water movement within one mikva is inconsequential, and the mikva is still viewed as stationary, so too we are not concerned with water movement between two connected boros (which are viewed as one mikva).
However, when the nekev hashoko is only partially full of water, no halachic connection exists between the two boros. This being so, the inevitable water movement in the nekev hashoko as a result of tevila renders the mikva zochalin and therefore invalid for tevila according to some Poskim. In extenuating circumstances or b’dieved a sheiloh should be asked.
The same invalidation applies if the water level is lower than the entire nekev hashoko, and the tevila causes the water to rise and partially fill the nekev hashoko.
This applies all mikvaos (i.e. keilim, men’s or a ladies mikva).
