No was wrong, I didn't post this. So now...
Life for the average Jew, in the average village, depended on access to the
mikvah. A man from the tribe of Levi, a son of Aaron could not assume his office as priest until he had gone through a mikvah. Before a person could be
tahor/ritually clean to enter the grounds of the Holy Temple in Jerusalem, he must be immersed in the
mikvah. The severest punishment was imposed on a person for entering the Temple area in the state of tomeh/ritual impurity. A woman in her monthly cycle was required to ware special clothing so all would know that she was in a state of
niddah (ritually unclean due to monthly cycle). She would not be
tahor/ritually clean until after entering the
mikvah. Immersion in a
mikvah is an integral part of conversion to Judaism. Without immersion conversion is not valid. There are many more times an immersion in a
mikvah is customary, we will endeavor to explore as many as space permits.
There are two basic parts of Torah, one is the written Torah consisting of the first five books of the Bible, with which we are all familiar. The second part of Torah is just as important but not as well known. It is what we call the Oral Torah or unwritten law. This was handed down orally from generation to generation for about 1,500 years. About the third century C.E. Oral Torah was put into writing by Rabbi Yehudah the Prince and is the foundation of Mishnah. The Talmud was formed after discussion and commentary was added. All Jewish law is derived from this Oral Torah. We might call it the "how to" book. Detail instructions on how to carry out all worship, the festivals, sacrifices, commandments, including ritual purification and preparing the mikvah are in Oral Torah.
http://www.hebroots.com/mikvah.html
Just to remind. I am not Hebraic Roots.