Upon entering the Temple Mount and the temple courts in the Second Temple period, Jews had to be ritually pure, as prescribed in the Mishna (The Mishna, Kelim 1.8-9). In most cases purification could be achieved by bathing in rainwater collected in a ritual bath (in Hebrew: miqveh, plural: miqva'ot). According to the Jewish law (Halakha), a miqveh must be attached to the ground, that is, not a pre-cast basin or bath resting on the ground; it must be filled with freely-flowing rainwater, not drawn water; the volume of water should be at least forty se'ah (500–1,000 litres); and the installation must be plastered to ensure that it is watertight.

Most miqva'ot were built in cellars; though this was not required by the Halakha, it assured privacy, as ritual immersion was performed in the nude. Moreover, darkness preserves the quality of the water, as prolonged exposure to sunlight promotes the growth of algae. Miqva'ot, like other water installations of the Second Temple period, were lined with a watertight plaster containing an admixture of ashes, which gave it its grayish color.

A flight of steps led down to the water. In many miqva'ot efforts were made to separate those going down to bathe, who were still impure, from those already cleansed, on their way up and out (for many kinds of impurity are transferred by mere contact). This was done by building a low parapet down the middle of the staircase, or by providing two openings, as described in the Mishna (The Mishna, Shekalim 8.2)