Bathtub Mikvaot and The Curious History of a Halakhic Libel

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Aryeh Klapper

In his haskamah (approbation) to Dr. Yitzḥak Frank’s Grammar for Gemara,[1] Rabbi Nathan Kamenetzky writes:

With regard to grammar, I note that my revered father זצ”ל held that its study is included in the מצוה of תלמוד תורה because its knowledge is crucial for reaching correct Halakhic conclusions. He cited a grammatical error which led a well-intentioned author to propose building a מקוה in every Jewish home. Ignorance of the gender of the noun אצבע in רמבם הלכות ספר תורה פט הט had led that individual to advocate מקוואות that were undersized and invalid; their use would have resulted in massive איסורי כרת. Knowledge of grammar is thus not פרפראות לחכמה, which the תוספות יו”ט defines as studies undertaken to enhance knowledge―which is not to be denigrated―but גופי הלכות, studies that affect Halakha.

Who was this “well-intentioned author”? Did he in fact advocate for obviously undersized mikvaot? Did his position result from grammatical ignorance? Does advocacy of home mikvaot necessarily entail advocacy for undersized mikvaot? Answering these questions requires some background.

Halakhah sets out detailed standards for a valid mikvah in terms of water supply, size, etc. (see Shulhan Arukh, Yoreh Deah 201-202). These standards historically made building a mikvah practical only for communities, which is why Halakhah declares the mikvah first priority for community construction.

The advent of indoor plumbing in the late nineteenth century opened the theoretical possibility of building mikvaot in ordinary private homes. Practically, however, the vast majority of Jewish women in the United States at that time did not immerse in any mikvah.[2]

In the early twentieth century, Rabbi David Miller of Oakland, California dedicated himself “to the revival of the observance of niddahtevilahmikvah.”[3] He theorized that women were uncomfortable immersing in public mikvaot for reasons of hygiene or modesty. (This discomfort may have been the product of improved private bathing facilities.) His proposed solution was “a mikvah in every home.” A successful contractor, he published reams of designs for mikvaot that (he certified) could be built cheaply and effectively by anyone and fit easily and attractively into living areas as well. They could even be disguised as cabinets or used as the frame for sofas, etc.

Rabbi Miller first published his designs in 1920 in a short Yiddish book titled Mikveh Israel. In 1930, he published a more ambitious English tome, The Secret of the Jew, which included hundreds of pages of exhortation, a review of the laws of mikvah construction, and his designs, of course. The Secret of the Jew was self-published and distributed for free in at least eleven editions before his death in 1939. Mikveh Israel included endorsements from Rabbi Shlomo Elchanan Jaffe and Rabbi Shimon Tzvi Elbaum,[4] and it was quoted extensively by prominent Chabad posek Rabbi Nissan Telushkin in 1947 in his Taharat ha-Mayim (and again in the 2nd expanded edition in 1950).

The “well-intentioned author” criticized by Rabbi Kamenetzky’s father was unquestionably Rabbi Miller. Did he in fact make the alleged grammatical error, and did it indeed result in his advocacy for undersized mikvaot? If not, why would such a libel have developed and spread?

Rabbi Miller’s home mikvaot were intended to be filled with ordinary municipal tap water. It is universally agreed that mikvah water must not have been stored in a keli (utensil) capable of holding water (Shulhan Arukh, Yoreh Deah 201:6). Such water is called she’uvin. The mikvah itself must also not be a keli. The Secret of the Jew contains extensive explanations of why tap water is not considered she’uvin (despite being piped from reservoirs and journeying through holding tanks and water meters) as well as detailed instructions for constructing a water-tight mikvah that is nonetheless not halakhically a keli.

Rabbi Miller’s approval of tap water mikvaot was not radical at the time. Rabbi Yossi Azose argues convincingly that communal mikvaot filled from municipal water supplies were common in the United States until at least the late 1950s.[5]

Sometime after Rabbi Miller’s death, however, Rabbi C.Y.L. Deutsch began an enduring and successful campaign to “upgrade” such mikvaot to systems that connect with rainwater pools (through a mechanism known as hashakah). There is no doubt that such systems offer significant halakhic advantages, and it is not hard to construct arguments for invalidating tap water mikvaot.

We can understand why supporters of Rabbi Deutsch’s campaign would be unhappy with Rabbi Miller’s proposal for home mikvaot, which assumed the halakhic validity of tap water mikvaot and advocated for their use even in communities with a public hashakah mikvah.[6]

Opponents of home immersion also note correctly that only total immersion is halakhically sufficient, and the vast majority of women cannot fully immerse themselves in standard-size bathtubs. (This is independent of the objective amount of water necessary for a valid mikvah.)

If one has not read Rabbi Miller’s books, it is reasonable to suppose that he was advocating for bathtub immersions―that is, for immersion in mikvaot that do not enable total immersion. After all, Halakhah does not require a mikvah to be used exclusively for religious purposes. There is no halakhic objection to using a mikvah as a bathtub. So why should there be an objection to using a bathtub as a mikvah?

It therefore makes sense that proponents of bathtub immersion cite Rabbi Miller as their precedent[7] and that opponents of tap water mikvaot accuse him of supporting bathtub immersion. One side sees bathtub mikvaot as an evocative symbol of opposition to stringencies that make halakhic observance difficult and empower rabbinic bureaucracies. Meanwhile, the other side uses Rabbi Miller’s alleged validation of bathtub immersions as a rhetorical weapon to cast support for tap water mikvaot in a negative light so that it seems absurd.

In fact, Rabbi Miller himself stridently rejected the use of bathtubs as mikvaot. A subchapter in The Secret of the Jew is titled “A Bathtub is not a Mikvah.” Both Mikveh Israel and The Secret of the Jew contain instructions for building a separate mikvah in one’s house.

How did this false impression start? Like most urban legends, it has a basis in fact. Let’s look at the Rambam cited by Rabbi Kamenetzky:

The width of the gudal[8] used in all these measurements and in all other Torah measurements is the etzba ha-beinoni. We have carefully calibrated its measurement and found that it is the width of seven medium barley grains placed side-by-side exactly, which is the equivalent of two barley grains in length. The term tefah everywhere equals four of these etzbaot, and the term amah equals six of those tefahim.[9]

Rabbi Kamenetzky asserts that Rabbi Miller did not correctly identify the gender of the word etzba. Why would this matter? The key is that the following word “ha-beinoni” is masculine. So if etzba is masculine, Rabbi Kamenetzky reasons, then the phrase should be read together: “the etzba, which is the beinoni,” or the middle finger. But if etzba is feminine, then it must be translated as “the etzba of the beinoni,” or “the etzba of the average person,” without telling us which finger is the etzba.

I do not disagree with Rabbi Kamenetzky about the importance of grammar. But grammarians become terrible interpreters when they assume that all writers share their sense of correct grammar. For interpretation, what matters is not what gender the words etzba and habeinoni have in “correct” Hebrew; rather, it is whether medieval Jewish texts assigned them a consistent gender.

The evidence is clear that they did not do this. For example,   On the other hand, Netziv―certainly a fine grammarian―writes in Meishiv Davar 1:20, “It seems that they were concerned to measure by a person with wider fingers than the average person, unlike Rambam, who wrote explicitly ‘ve-hu ha-beinoni,’ meaning ‘of the average person.’”

Plainly, both understandings of etzba ha-beinoni are possible. In fact, both have long histories.

Rabbi Kamenetzky presumably assigned etzba as feminine, as it is in Tanakh, and adopted Netziv’s interpretation―“of the average person.” He charged Rabbi Miller with the grammatical error of seeing ha-beinoni as modifying etzba and therefore of mistakenly identifying it with the middle finger. He further claimed that this “error” led Rabbi Miller to advocate for mikvaot that were too small.

When I first heard this charge against Rabbi Miller, it seemed obviously incorrect. No one disputes that the minimal halakhic measurement for a kosher mikvah is at least enough water for an ordinary person to fully immerse. Any measurement too small to enable this would be useless, and any measurement that enables this is plausible.

Moreover, the Talmud (Eruvin 14b) provides an objective volume measurement for a mikvah―it must be three amot by one amah by one amah, or three cubic amot. Since the range of positions as to the length of the halakhic amah ranges from approximately 18 to approximately 24 inches, Rabbi Miller had an easy way of checking his calculations. A 24 inch amah yields a 24-cubic-foot mikvah, and an 18 inch amah yields a 10.125-cubic-foot mikvah. Presumably, Rabbi Miller’s number fell somewhere in that range.

The mystery deepened when I looked up Rabbi Miller’s book[10] and discovered the following:

  1. he advocated for a 24-cubic-foot mikvah, the largest possible size, and
  2. he understood the phrase in Rambam exactly as Netziv and Rabbi Kamenetsky did.

Moreover, as Rabbi Miller was certainly aware, Rambam in other places makes perfectly clear how to measure the relevant etzba. In Hilkhot Shabbat 17:36, Hilkhot Tzitzit 1:6, and Hilkhot Nesiat Kapayim 15:4, he writes that any etzba mentioned with regard to measurement refers to the thumb, not to the middle finger. (In fact, though Rabbi Miller was not aware of this, the word etzba is not present in any manuscript of Hilkhot Sefer Torah 9:9. Assuming that this is the correct text, there would be no ambiguity at all.)

So, what was the basis of Rabbi Kamenetzky’s charge?

Rabbi Ezra Schwartz of RIETS, my son’s wonderful rebbe, put me on to the truth. In 1938, Rabbi Miller became frustrated that his efforts to popularize home mikvaot had not been met with sufficient success. He decided that more people would build them if they took up less space. So, he recalculated. The upshot was that for the eleventh edition, he shrank the required size of a mikvah from 24 cubic feet = 179.53 gallons to 10.777 cubic feet = 80.57 gallons.

Rabbi Miller acknowledges in this last edition that friends advised him to avoid controversy by adopting the Arukh ha-Shulhan’s measurements instead, which he presents as 15.6 cubic feet = 116.7 gallons. He decided regardless to advocate for the smallest possible measurement in order to make the mitzvah as accessible as possible. Furthermore, he writes that empirical observation (he tried it himself) will demonstrate that a mikvah of his recommended size is sufficient for full immersion. He reports sending his revision to a broad range of scholars and receiving no factual rebuttals.

And therein lies the rub. Rabbi Miller also does not report receiving any letters endorsing his revised measurement. He acknowledges that it is much smaller than any approved European mikvah. It seems likely to me that none of the approbations to his earlier editions would have approved the revision, and it also seems likely that he did not give anyone the option of withdrawing their previous approbations.

Standard mikvaot of course use larger measures than Rabbi Miller’s as to avoid taking chances. There is no way to know whether adopting the smaller measurement would have generated a wave of home mikvah-building and significantly greater observance of the laws of family purity. My suspicion is that vanishingly few home mikvaot of any size were built to his design, but I would welcome evidence to the contrary.

Rabbi Miller’s new position validated mikvaot that were at least within shouting range of the capacity of the very largest bathtubs[11] (remembering that to be valid, a mikvah must be able to hold its full measure of water while the person is fully immersed). While the eleventh edition of his book still adamantly declared that a bathtub could not serve as a mikvah,[12] it became superficially plausible to accuse him of approving bathtub mikvaot (and to cite him as if he approved such mikvaot).

The stage was thus set for the later unfair dismissal of his work via such accusations as Rabbi Kamenetzky’s. Rabbi Miller’s ideas for home tap-water mikvaot may or may not have been plausible in his time, and they may or may not have any relevance in our time. But, his halakhic scholarship deserves respect and consideration.

[1] Yitzḥak Frank, Grammar for Gemara and Targum Onkelos: An Introduction to Aramaic, 3rd ed. (Jerusalem: Ariel United Israel Institutes, 2016), viii.

[2] Beth Wenger, “Mikveh,” The Encyclopedia of Jewish Women, Jewish Women’s Archive, March 20, 2009,

[3] See David Miller, The Secret of the Jew (New York: Rabbi David Miller Foundation, 1938), v.

[4] According to Rabbi Yossi Azose, there is also an approbation from Rabbi Moshe Zevulun Margoliot (RaMaZ), but I have not found this. See fn14 in Yossi Azose, “The Use of Municipal City Water for a Mikveh and the Case Study of the Seattle Rabbinate in the 1950s,” Institute for Jewish Ideas and Ideals, August 10, 2017,

[5] Ibid., 3.

[6] David Miller, The Secret of the Jew, 3rd ed. (New York: Rabbi David Miller Foundation, 1938), 277-282.

[7] Haim Ovadia, “Mikveh in Every Home,” Merrimack Valley Havurah (blog), August 10, 2017,

[8] Gudal generally means “thumb.” However, see Rabbeinu Bahye, Leviticus 8:23 for a position identifying it as the pinky. See also Bartenura to Mishnah Eruvin 1:1.

[9] All translations in the article are my own.

[10]David Miller, The Secret of the Jew, 3rd ed. (New York: Rabbi David Miller Foundation, 1938), 359.

[11] My home’s ordinary five-foot bathtub contains slightly over 8 cubic feet, or around 60 gallons.

[12] For this author’s explanation of why Rabbi Miller invalidated bathtub mikvaot for reasons other than size, please see Aryeh Klapper, “Can a Bathtub be a Mikveh?” in CMTL Shavuot Reader 2020 Edition, Center for Modern Torah Leadership, May 28, 2020,, 8-10.

Aryeh Klapper is Dean of the Center for Modern Torah Leadership, which develops present and future Modern Orthodox leaders through unique programs of intense Talmud Torah that catalyze intellectual creativity and educational innovation. CMTL brings rigorous traditional scholarship, interdisciplinary openness, and a deeply humanist understanding of halakhah to every aspect of Jewish and public life.