Immersion in fresh water is the basic form of purification in Jewish Law. According to Jewish law, women must immerse themselves, typically in a mikvah (ritual bath of gathered rainwater), after their menstrual period. By contrast, ritual immersion for men is not a matter of Jewish law but is customary among the Hassidim, especially before the Sabbath and holidays and in preparation for morning prayers. Freshwater springs located in the Jerusalem hills are popular sites for male ritual immersion.