MIḲWEH (rabbinic Hebrew, miḳwah; plural, miḳwa'ot):
Literally, a "collection," a "collected mass," especially of water (Gen. i. 10; Ex. vii. 19; Lev. xi. 36; comp. Isa. xxii. 11). Because of the use made of this word in connection with ritual purification (Lev. xi. 36), it has become the term commonly used to designate the ritual bath. In all cases of ritual impurity it was necessary for the person or object to be immersed in a bath built in accordance with the rules laid down by the Rabbis (see Ablution; Baths; Purity). Since the Dispersion the custom of observing the laws of purity has on the whole fallen into desuetude, except in the case of the impure woman (see Niddah). With regard to her the laws are still observed in most Orthodox communities, and therefore the ritual miḳweh is still a necessary institution there. Some observant Jews, especially among the Ḥasidim, immerse themselves in the miḳweh in cases also of impurity other than niddah.Size and Contents.
In order to be ritually fit for use, the miḳweh must contain sufficient water to cover entirely the body of a man of average size. The Rabbis estimated that the miḳweh should be 3 cubits long, 1 cubit wide, and 1 cubit deep (= 44,118.375 widths of the thumb; Shulḥan 'Aruk, Yoreh De'ah, 201, 1), containing 40 se'ahs of water ('Er. 4b; Yoma 31a; et al.; comp. Pes. R. 82b). The se'ah is described as a measure holding 144 eggs (Num. R. xviii. 17), i.e., 24 logs (= 24 pints = 3 gallons approximately; see Weights and Measures), so that the miḳweh must contain at least 120 gallons of water.
The water of the miḳweh must come from a natural spring or from a river that has its source in a natural spring (Sifra to Lev. xi. 36). A tank filled by the rain may be used as a miḳweh, although some authorities forbid the use of a pool which is full of water in the rainy season and dried up in the summer (Maimonides, "Yad," Miḳwa'ot, iii. 1-3; Yoreh De'ah, 201, 2, Isserles' gloss). A miḳweh derived from snow, ice, or hail is regarded by the authorities as ritually fit for use, although there is a difference of opinion with regard to the manner of melting the snow (Miḳ. vii. 1; Yoreh De'ah, 201, 30; comp. SHaK and "Pitḥe Teshubah," ad loc. ; see also "Ḥatam Sofer" on Yoreh De'ah, 200, 213).
The water contained in the miḳweh must not have passed through a vessel of such a form that it can hold objects placed in it. Pipes open on both sides are not regarded as vessels in the accepted meaning (Miḳ. iv. 1; "Yad," l.c. vi. 1, 2). In large cities, where the water-supply comes through underground pipes and where water is measured by meters, many points involving legal technicalities must be observed in the construction of a miḳweh. In order to observe these the following is the process followed by some rabbis in the building of a miḳweh in a large city: A small miḳweh, with a capacity of 40 se'ahs, is built near a large tank, and a conduit is made from the smaller tank that leads to an opening in the larger. The small tank or miḳweh is first filled with snow or ice; when the snow or ice fills it to the brim the aperture leading into the large tank is opened, and water is poured over the ice or snow and passes into the large tank. Thus the original miḳweh is made from snow or ice, about the ritual fitness of which there is no doubt, and then as much water is added as is needed (Yoreh De'ah, 201, 36; "Resp. Rosh," 30, 31; Caro, "Abḳat Rokel," pp. 50, 51, 56; "Noda' bi-Yehudah," 2d series, Yoreh De'ah, 136, 137; "Ḥatam Sofer," ib. 198, 199, 203, 204, 206; Berlin, "Meshib Dabar," ii. 38).
If three logs (= pints) of water be poured into a miḳweh which does not have the prescribed measure of water, the miḳweh becomes unfit for ritual use, even though the 40 se'ahs are later completed in a legitimate manner. In such a case, the miḳweh has to be emptied and then refilled in the prescribed way. If, however, the miḳweh has the required measure, water from other sources may be poured into it without impairing its ritual fitness (Miḳ. iii.; "Yad," l.c. v. ; Yoreh De'ah, 201, 15 et seq.).
The ritual bath always formed one of the most important institutions of a Jewish community (see Abrahams, "Jewish Life in the Middle Ages," p. 73). In urgent cases it was permitted even to sell a synagogue in order to erect a miḳweh (Berlin, "Meshib Dabar," ii. 45).