Private. Mystical. Difficult.

These are just some of the words that can be used to describe a Jewish woman's observance of taharat hamishpachah (laws of family purity).

Taharat hamishpachah is one of the three mitzvot assigned almost exclusively to women. The other two are taking challah (removing a portion of challah dough in memory of the priestly tribe) and lighting candles.

The laws of taharat hamishpachah prohibit sexual intercourse and other sexual contact during a woman's menses and for seven days following, culminating in immersion in a mikveh (ritual bath).

The laws surrounding niddah (a woman's ritually impure state) and mikveh come directly from the Bible:

*Leviticus 15:19: A woman, when she is done with a flow, her flow being of blood from her flesh, seven days shall she remain in her state of being apart. Anyone who touches her is to remain tamei (ritually unclean) until sunset.

*Leviticus 18:19: To a woman, during her time of tuma (ritual uncleanliness) you are not to come near, exposing her nakedness.

*Leviticus 20:18: A man who lies with a woman having her flow, exposing her nakedness, her source he has laid naked and she has exposed her source of blood; the two of them are to be cut off from amid their kinspeople.

The mitzvah of taharat hamishpachah is so important in Judaism that the Talmud states that if communal resources are stretched and the community can either build a synagogue or a mikveh, the ritual bath comes first. Communal leaders are also enjoined to sell their Torah scroll if they must to pay for a mikveh.

The water in the mikveh must be "live" water; it must come directly from a lake or river or rain, without benefit of taps or pipes.

The mikveh is not a place to get clean. In fact, before a woman immerses herself in the ritual bath she must soak in a bathtub or take a long shower. She must cut her nails and clean under them for dirt, remove makeup, brush and floss her teeth, comb her hair free of knots and remove the loose hairs. This is done to remove any barriers between the woman and the water.

Every part of the woman's body must be immersed, observed discreetly by the mikveh attendant, another female. After the first immersion, a blessing is recited, and the woman dips two more times.

In her book, "How to Run a Traditional Jewish Household," Jewish feminist Blu Greenberg reflects on the importance of the laws of family purity.

"Taharat hamishpacha implies that sex is a special part of marriage, but not the only part. Early on, one learns that sex is not all there is to love, that not every newlywed spat can be settled in bed, that for almost half a month niddah requires of us to develop other, more difficult, more sophisticated modes of communication.

"A couple in love who observe niddah is forced to discover new techniques to express peaks of emotion; such a couple more readily understands the power of a glance, a word, a thoughtful gesture."

Greenberg points out that although the onus of the mitzvah of taharat hamishpachah is on the woman, it takes mutual consent and understanding. Otherwise, it becomes a monthly contest of wills, with no real winner.