Mikvah ‘Bor Al Gabei Bor’

Ask the Rov: What is a Chabad ‘Bor Al Gabei Bor’ mikvah and what is the significance of it?

By Rabbi Chaim Hillel Raskin – Rov of Anash in Petach Tikvah

In earlier times, mikvaos were often natural springs (maayan) that flowed from under the ground. However, as Yidden spread out to live in many places where springs weren’t accessible for tevilah, the need to build rainwater mikvaos grew.

The issue with such a mikvah is that when the rainwater gets dirty, it can’t be cleaned or switched easily. The solution is to connect a pool of regular water to a pool of rainwater, thus making it kosher. This way, the immersion pool (bor hatevila) can be clean, and it will still be considered as immersing in kosher rainwater.

In general, there are three methods of kashering the regular water:

(1) Zeriah (“sowing”) – the city water flows over a pit containing 40 se’ah of rainwater and then continues on its path into the bor hatevila. Every time one needs to refill the mikvah, the same procedure can be used.

However, if the city water flowing over the zeriah pit doesn’t stop to rest, some question if it kashers the water.1 Also, when relying on this method alone, the bor hatevila must be completely dry before each time it’s filled up.2

(2) Hashaka (“kissing”) – the two full pools are connected with a hole the size of shefoferes hanod (the opening of a waterskin), big enough for two fingers to rotate. The hole is usually kept sealed with a plug to prevent the waters from interchanging. However, some require the connection to be open during tevilah.3

The challenge with this method is that if one forgets to open the connection, the immersion pool won’t be kosher.4 Additionally, the water in the two pools must be connected when the water levels are equal; otherwise, the connection is via zochalin (“flowing water”) and is invalid.5

According to the Raavad, the pool of rainwater can only kasher the city water as long as the majority of 40 se’ah of the original rainwater remains. In both of the abovementioned methods, the rainwater pool will be replaced by city water within a short period of time.6 While this opinion is not codified in Shulchan Aruch, we try to be mehader to have a mikvah meet all standards.

(3) Bor al gabei bor – a bottom pool holds the rainwater, the top pool has city water, and they touch through a hole (preferably a tefach by tefach).

With this design, championed by the Rebbe Rashab, the static connection is top to bottom and warm to cold, causing the water to mix at a much slower pace, satisfying the Raavad’s concern.7 (Additionally, since they are top to bottom, it’s like one big mikvah, and one is considered to be immersing in the actual rainwater.8)

Yet, since the water does mix over time, if one wishes to achieve this benefit, one must change the water from time to time (the exact timing is questionable). Yet, it should only be done under the supervision of a knowledgeable mikvah expert, since doing it wrong can invalidate the mikvah entirely.

See Sources (open PDF)

From The Weekly Farbrengen by Merkaz Anash

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