Whenever most misvot are performed our rabbis instituted the idea of pronouncing a blessing of God. The overall purpose of the blessing is to praise God and at the same time to heighten one's awareness of God's beneficence. The blessing upon immersion in the mikveh has the same structure as the blessing said upon the performance of many misvot. It contains the recognition that misvot are means of sanctifying us-- of raising us to a higher human/spiritual level. The misvot, though sometimes difficult to perform, have the consequence of sanctifying us. The pronouncement of the blessing reminds us of this sanctification.
1. Before a woman immerses, while she is still in her robe, she should make the blessing required before immersion. Then without speaking she should remove her robe and immerse.
2. The blessing is : Baruch atta adonay elohenu melekh ha'olam, asher qiddeshanu bemisvotav vessivannu 'al hatebilah. Which means--"You are blessed, Hashem, our God, King of the Universe, who has sanctified us through His commandments and commanded us concerning immersion."
3. The blessing should be recited in the room next to the mikveh pool, (a room where people do not bathe or stand unclothed) and not in the room of the mikveh pool itself.
4. If a woman forgot to say this blessing she need not immerse again. One should not make this blessing after she immerses. The predominant Ashkenazi custom is to immerse once and then make the blessing.
5. A bride who is immersing for the first time does not say the blessing "Shehehianu."