When a woman immerses in a Mikveh, another woman – generally called a "Balanit" – must be present to observe the immersion and ensure that all of the woman’s hair is submerged in the water. If even a single strand of hair remains above the water, the immersion is invalid and must be repeated. Even if there is some doubt as to whether all the hair was submerged, the woman must repeat the immersion.
The woman immersing in a Mikveh should not hold another woman’s hand during the immersion. If the woman requires assistance during the immersion, such as if she is ill or injured, then the accompanying woman should thrust her hands into the Mikveh so they become wet with Mikveh water, and then loosely hold the woman’s hand during the immersion. She should not hold the woman’s hand tightly.
The woman immersing in a Mikveh should not immerse in an upright position, or in a bowing position. She should rather lean forward slightly, in the position women assume while kneading dough.
The woman does not have to open her mouth in the water, but she should not tightly clench her mouth shut during the immersion. Instead, her lips should touch each other loosely, so that the outer part of the lips comes in contact with the water. If her mouth is clenched tightly during the immersion, she must immerse again. Clenching her teeth together, however, does not invalidate the immersion. Her eyes, too, should be loosely closed during the immersion, so that the eyelids and entire area outside and around the eyes come in direct contact with the water. Her eyes should neither be tightly shut nor kept open during the immersion.
Summary: When a woman immerses in a Mikveh, another woman must be present to ensure that all her hair is submerged in the water. The woman should lean forward slightly during the immersion, and her eyes and mouth should be loosely closed, as opposed to tightly clenched. The woman should not hold another woman’s hand during the immersion.
