Editing Hovaya Al Yedei Tahara (Creation Through Purity)

One of the fundamental rules regarding mikvaos is "Hovaya Al Yedei Tahara" (creation through purity), which is a Torah commandment derived from the verse "But a spring or a cistern, a gathering of water, shall be pure." Our Sages interpreted the words "shall be pure" to mean that the creation of the mikvah must be done through pure means - meaning through items that cannot receive tumah (ritual impurity).

== Practical Implications ==
This halacha has many practical implications. The mikvah water must not enter through any item that can receive tumah. Therefore, if one places metal, food, drink, or any vessel that can receive tumah in the place where water enters the immersion pool, the water becomes invalid for immersion. For this reason, a person is also forbidden from directly throwing water into the immersion pool, unless it is done through hamshachah (drawn water), where the water is poured at some distance from the immersion pool and then flows into the mikvah.

Additionally, the pool itself must not be made from materials that can receive tumah - not just in its entirety but even partially. If even part of the immersion pool's walls is made from material that can receive tumah and supports the mikvah, the mikvah is invalid for immersion.

The poskim (halachic authorities) address two concerning situations: The more severe one is when there is a hole at the bottom of the pool that supports all the water. The Divrei Chaim of Sanz addressed such a mikvah: "At the floor of the mikvah there is a large hole for draining the water to clean the mikvah, with a metal plug blocking this hole except when needed for cleaning the pool. When this metal plug is removed, the pool remains empty without water - this is the essential construction of these mikvaos as I have seen in several places. According to this, all the water in the mikvah is supported by this metal, meaning the entire existence of the mikvah depends on something that can receive tumah, as simple metal vessels can receive tumah."

== The Rebbe's Instructions ==
The Rebbe addresses this issue with particular stringency:

"Regarding what was written about the mikvah - although one word is unclear in the writing, it appears to refer to water leaving and being blocked by an iron stopper that blocks a hole in the mikvah floor. I was shocked to read this, and perhaps this is not the correct interpretation. There has already been outcry against the allowance of initially making it with intent to establish it... Surely you have a copy of the letter from the Rebbe Rashab who refused to allow even rubber (kautchuk) to block the hole due to those who hold it can receive tumah, and advised making stoppers in several places from simple wooden vessels made extremely smooth. Since it's difficult to precisely fit and seal between wood and stone, the solution is to make part of the floor corner from wood with a hole in it sealed by a wooden stopper, as wood-to-wood sealing is easier. But what's even better, and has been practiced everywhere within my reach, is not to have any hole in the floor at all, and to remove the water using a pump (nasos), preferably using a pump called siphon, as is known to those who deal with such matters."

In his letter, the Rebbe also mentions the Rebbe Rashab's opinion against using rubber plugs to seal the hole, since there is an opinion that rubber can also receive tumah.

In practice, this stringency does not apply to mikvaos where the hashakah (connection) hole is on the side, since in such cases the vessel is not made to serve as a receptacle or for stepping on, and therefore cannot receive tumah. However, in a Chabad-style mikvah built with the bor al gabei bor (pool above pool) method, where the hashakah hole is in the floor of the upper mikvah, the Rebbe notes:

"Regarding what you wrote that it wasn't designated for stepping - one can simply say that since it blocks a hole in the floor, besides that sometimes only a small part protrudes above the floor and consequently the one immersing or blocking the hole steps on it either accidentally or intentionally to seal the hole properly, even if it protrudes more, sometimes people use it to stand on to reach something above the mikvah walls and the like. Obviously if they step on it even accidentally, it becomes part of the floor and is designated as such. Moreover, if they step on it to properly seal the hole, it ultimately becomes part of the floor designated for stepping, and this too is called designation for stepping."

Chabad Chassidus is very strict about this matter. For example, Chabad leaders prohibited the use of plastic, despite it being common in mikvaos worldwide and most poskim ruling that plastic (primarily made from petroleum) cannot receive tumah. However, the Rebbe prohibited its use: "...regarding your letter about nylon and plastic - it seems (most likely) there are variations (now, and changing from time to time) regarding what these are made from. Since the Rebbe Rashab considers rubber something that can receive tumah - these should not be used either..."