Mikvah construction methods explained

Every kosher mikvah depends on how the immersion pool connects to a reservoir of natural rainwater, and there are three classical methods of building that connection. Each is valid when executed correctly under rabbinic supervision, and the choice shapes the design and the long-term reliability of the mikvah. Here is a clear overview.

Note: this is a general explanation, not a halachic ruling. Every mikvah must be built under the supervision of a qualified rav, and practical decisions belong to the supervising rabbi.

The foundation: 40 se'ah and the bor

A kosher mikvah requires a minimum of forty se'ah of valid water, a measure derived from the Torah and codified in the Shulchan Aruch. Because it is impractical to refill a mikvah with rainwater alone, mikvaos are built with a reservoir of rainwater, the bor, connected to the immersion pool so that ordinary tap water becomes valid through contact with the rainwater. The three methods are three ways of making that connection.

Hashaka, the kissing method

In hashaka, two pools are built side by side, connected by an opening in the dividing wall at least the width of a shfoferes hanod. The rainwater pool and the immersion pool touch through that opening, and the contact, the kiss, renders the tap water valid. The opening must be positioned at the correct height relative to the water levels. It is the most historically common method.

Zeriah, the sowing method

In zeriah, rainwater is collected in a reservoir, and incoming tap water passes through or over it so that it is considered sown into the ground and made valid. An advantage is that tap water becomes kosher on contact and no stopper is involved, so the rav does not have to worry about whether a stopper was removed. It carries its own technical considerations the supervising rabbi accounts for.

Bor al gabai bor, the Chabad method

In bor al gabai bor, literally one bor on top of another, the immersion pool sits directly above the rainwater bor, connected by openings in the floor. Because the upper pool is a continuation of the rainwater below, someone immersing is, in effect, immersing in the rainwater itself. It is widely considered the most foolproof method and is favored in Chabad communities following the approach of the Rashab. It requires no additional side pools.

Which method is right for your mikvah?

• Hashaka: side-by-side pools connected by an opening; the most traditional approach.
• Zeriah: incoming water sown through rainwater; no stopper to manage.
• Bor al gabai bor: immersion pool above the rainwater; foolproof; favored in Chabad.

We design and build to whichever method your supervising rav prefers, executed to the highest standard. The method is a halachic decision; our job is to engineer it flawlessly and wrap it in a beautiful, dignified facility.