Finishing menses and counting seven clean days are necessary for the cessation of the niddah status, but are not sufficient. Even if years have gone by since the last menses, a woman retains her status of niddah with all its attendant prohibitions until she immerses properly in a kosher mikveh. Proper immersion in a mikveh requires that a woman's entire body, including all of her hair, must be submerged in the water at one time. In general, anything that adheres to the body or hair and prevents contact with the water invalidates the immersion. Such a barrier is called a chatzitzah.
Mikveh Immersion Procedure
During immersion, a woman's entire body and all of her hair must be in simultaneous contact with the mikveh water. Therefore, the ideal position for immersion is "as if she is weaving or nursing her child" – slightly crouched, arms extended, hands open with the fingers slightly separated, eyes and mouth gently closed, but NOT clenched – so that the mikveh water reaches every part of her body. (The eyes and the inside of the mouth must be free of chatzitzot, but need not come into contact with the mikveh water.) A woman who has difficulty assuming the recommended position should wet all parts of her body with the mikveh water and then immerse in any position in which her body and hair are completely submerged. The custom in Chabad is to immerse while spread out "like a fish".
Because complete immersion requires relatively deep water, one generally walks down stairs into the mikveh. If a woman has difficulty with stairs, arrangements can be made to assist her.
Upon immersing in the mikveh, one recites the bracha (blessing) "… asher kideshanu bemitzvotav vetzivanu al hatevilah…Who has sanctified us with His commandments and commanded us on immersion." Many Sephardic women recite this bracha while wearing a robe, and then undress and immerse in the mikveh. This is in accordance with the general practice that a bracha should immediately precede the performance of a mitzvah. The prevalent Ashkenazic custom, however, is to immerse once, recite the bracha while standing in the mikveh with the water at least waist-high, and then immerse again. Although one may not normally recite a bracha while undressed, in this case the water is considered a sufficient covering. One should not look down into the water while reciting the blessing. Some women also cross their arms below the heart to separate the upper body from the lower body, and some cover their hair with a cloth.
A woman must immerse at least once after she recites the bracha. Some women have the custom to immerse additional times or to recite additional prayers.
Mikveh etiquette varies somewhat among communities. The following guidelines should be applicable in most situations.
Although immersion must take place after dark, most mikvaot open for preparation shortly before sunset (see Where to Prepare for Mikveh Immersion). The mikveh's opening and closing times should be verified beforehand (hours will generally be shorter on Shabbat and Yom Tov than during the week). Some mikvaot can make arrangements in advance for immersion after the usual closing time.
Large mikvaot generally operate on a walk-in basis, but appointments may be necessary in smaller communities. Some mikvaot also require appointments for immersion on Shabbat or Yom Tov.
It is proper not to disclose publicly the fact that a woman is immersing in the mikveh. Therefore, one should not reveal the names of other women one meets in the parking lot or waiting room. Similarly, a husband should not arrange to meet his wife right outside the mikveh, where he may encounter other women.