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Immersion is done at night after the completion of the seven clean days. A kosher immersion requires the entire body to be immersed at once. If a finger or even one hair is not in the water, the immersion is invalid. Since a woman cannot see herself, and there is a concern that some hair or part of her body might not go underwater, it is customary to have a mikveh attendant present to watch and make sure the immersion is done properly. The stance taken for immersion is meant to ensure that water will come into contact with all parts of the body – knees gently bent, feet apart, and hands stretched out in front of the body, with nothing scrunched up.
The widespread custom is for a woman to start by immersing once to wet her body. After doing so, she lifts her head out of the water and makes the following blessing: “Blessed are You, Lord our God, King of the Universe, Who sanctified us with His mitzvot and commanded us to immerse.” She then immerses again and becomes pure.
