Source
In
Jewish ritual law, the Mikvah (Mik-va) is a
ritual bath of natural
water of at least 40 "Se'ah", a talmudic liquid measure, depending on the authority, totals either 750 or 920 liters. Natural water, or "Mayim Chaim", (lit. Living Waters) is water that has not been in a vessel, which typically means it is either collected rain water, or a natural
lake or body of water.
The source for the concept of mikvah is scriptural, when the verses in Leviticus discuss the need for a leper to "wash in water" and for their clothes, etc. to be immersed, while the amount discussed comes from a discussion in the Talmud about how much water is needed to cover the entire body, as is implied from the verse (Leviticus 16, 17) "And wash in water the entire body."
Usage
The sages, in the
Talmud discuss many situations where a mikveh is required; purifying vessels, lepers, and many different requirements for ritual purity in connection to the
Bais HaMikdash, for example before a
Priest entered the temples to do the service.
The primary modern usage of a mikvah, however, and the reason that one is found in any jewish community, is Ritual Purity in relation to sexual relationships; A woman, after the onset of bleeding during her menstrual period, cannot touch her husband (nor, clearly, can he touch her) for a minimum of 12 days, (7 days after the blood stops, which period cannot start for a minimum 5 days) following which she must immerse herself in the mikvah before becoming purified. Similarly, after giving birth, a woman is impure for 40 or 80 days.
The immersion in the mikvah must not be buffered, and the water must come in contact with the entire body at once. This means that a person must shower before entering the mikvah, making sure they have no bandaids or other things on their body.
Practical Issues
The construction of a Mikvah is a prerequisite for any
Jewish community; The need, according to
Halacha preempts that of having even a
Torah scroll. The building of a mikvah, however, is a task that takes a very significant amount of expertise. The collection of the water, typically from
rain, must be done without using any pipes or other enclosed structure; the water must collect in the basin itself. This means that the building housing the mikveh is normally built with a roof designed to collect the water, sloped so that the water will collect above an opening which will allow the water to flow naturally in.
Once the requisite 40 se'ah of water is collected, the mikveh can begin functioning, and practical problems determine the structure of the mikvah. Once the mikvah is "Kosher" it is not a problem to add water that is collected in vessels, so the practical considerations typically become paramount; because the pool of water itself becomes dirty, a very specific system is used; two seperate bodies of water exist, first the actual "Mikvah" with the collected rainwater, then the pool in which people immerse themselves. The two are connected by a small opening, and the immersion pool is drained and cleaned periodically, joing with the Mikvah waters when full and becoming part of the actual mikvah.
Of course, the idea of Mikvah is not limited to women: men go to the mikvah at least yearly, before yom kippur, and many do so more frequently, either before each holiday, weekly before Shabbos, or daily. The mikvah, due to modesty, cannot be shared by men and women, and is either used by women at night and men in the mornings, or in larger communities, seperate mikvahs typically exist. Another seperate mikvah may exist for vessels made of materials that must be immersed before use, such as glass and metal, as a question of Kashrus