Immersion on Shabbat and Yom Tov
Many elements of chafifah (preparations for immersion), are prohibited or restricted on Shabbat and Yom Tov. Therefore, a woman who plans to immerse in the mikveh on Friday night or the night of Yom Tov should complete her preparations at home before she lights candles. This includes bathing, washing and combing hair, and cutting nails. Please see Chafifah on Yom Tov for a discussion of preparation during a two-day Yom Tov or when Shabbat and Yom Tov come one after the other.
At the mikveh, she should wet her body and hair prior to immersing. This prevents hair from floating on top of the water, and ensures that all parts of her body will be in contact with water during her immersion. During the week, women usually wet themselves in the shower just before immersion. But bathing on Shabbat is normally forbidden, particularly in warm water. Furthermore, most baths and showers do not allow for the use of hot water on Shabbat because more water is automatically heated up (this is prohibited on Shabbat but not on Yom Tov). Therefore, rather than taking a cold shower, many women immerse once in the previously-warmed mikveh to wet themselves before the halachically significant immersion. Some mikvaot, however, are equipped with showers designed for use on Shabbat. One should clarify the proper procedure with the mikveh attendant before entering the preparation room.
On Shabbat and Yom Tov, just as on any other day, a woman needs to visually inspect herself for barriers before immersing. If she finds a problem, she should ask the mikveh attendant how to proceed. Due to the laws of Shabbat and Yom Tov, the procedures may be different than on a weekday.