A mikve is a ritual immersion bath which restores the purity required by religious law. The Torah records a series of situations in which a purifying bath is necessary, e.g. after infectious diseases, after handling corpses, and for women after menstruation.
The construction of the mikve is governed by religious law. The mikve must have a certain minimum size and the water must be "flowing", i.e. groundwater or collected rainwater. The mikve must hold at least 800 litres of water. There were several mikvot in the Judengasse. The oldest was in the Kaltes Bad, which later became the dance hall, and in 1711 was rebuilt as the Steinernes Haus. The new Kaltes Bad was built behind the synagogue in 1587. It and was burned down in both 1711 and 1721. A further bath house, the Women's New Cold Bath located behind the synagogue, received building permission in 1602. Because sexual relations with a woman after menstruation or childbirth are forbidden by religious law until she has taken a purifying bath in the mikve, the mikve has retained its significance up till the present day. Every Jewish community had and still has at least one mikve conforming to religious requirements. The mikve is also used to immerse new dishes before they can be used.