The mikveh is the least discussed and most consequential piece of Jewish infrastructure. Jewish law requires a community to build one before it builds a synagogue, and permits selling a Torah scroll to fund it. The pool must contain at least forty se'ah of water, of which a defined portion must be rainwater or spring water rather than drawn — modern mikvaot are engineered around this, with a rainwater reservoir connected to a treated pool. The main users are married women, immersing after menstruation and the seven clean days that follow, which ends a separation of roughly twelve days a month during which a couple do not touch. Converts immerse once, and it is the moment of conversion. Hasidic men immerse before Shabbat and festivals, and many Sephardi men do too. Grooms immerse before the wedding; new vessels are immersed before use. Non-Orthodox Judaism largely abandoned the practice in the twentieth century and has been reclaiming it since the 1990s for purposes it was never used for — after divorce, after miscarriage, at the end of cancer treatment, before a significant birthday — which Orthodox authorities regard as a category error and which has become one of the more creative areas of liberal Jewish practice. Separately, the treatment of women by mikveh attendants and the question of state supervision have been repeatedly litigated in Israel.