Thursday, August 23, 2012

Berachot 22a: How long is a 9 kav shower?

On Berachot daf 22a:
Our Rabbis taught: A ba'al keri on whom nine kabs17  of water have been thrown is clean. Nahum a man of Gimzu18  whispered it to R. Akiba, and R. Akiba whispered it to Ben 'Azzai, and Ben 'Azzai went forth and repeated it to the disciples in public. Two Amoraim in the West differed in regard to this, R. Jose b. Abin and R. Jose b. Zebida. One stated: He repeated it, and one taught, He whispered it. The one who taught 'he repeated it' held that the reason [for the concession] was to prevent neglect of the Torah and of procreation. The one who taught 'he whispered it' thought that the reason was in order that scholars might not always be with their wives like cocks.19
The conclusion of the Rif is as follows:
There is one who said that this they they said "They have abolished immersion" is in regard to both words of Torah and prayer. And there is one who said that this is only as regards to words of Torah, but in regard to prayer you need immersion. And not immersion {tevila} specifically but rather washing in 9 kav. And Rabbenu Hai Gaon wrote that since the gemara does not deal with this matter, we should take the custom of all Israel that all Baal Keri, even if they have no water, should not pray until they wash.
Practically, though, nowadays most (non-chassidic) people do not worry about tumat keri for any purpose whatsoever.

But see this practical halacha discussion by Rabbi Chaim Eisenstein:

Now Playing:
Halacha & the Daily Daf: Berachos 22 -- Tefilla and Talmud Torah for a Baal Keri
Rabbi Chaim Eisenstein
Speaker:Rabbi Chaim EisensteinGiven On:Monday August 20, 2012

Assuming one want to be machmir for this position, and also hold that nine kav is sufficient, then there is good reason to assume that a shower is a valid way of fulfilling this. But then, how long must the shower be to get nine kav?

Here, from Wikipedia, are the water standards for showers in the US. But one could turn a shower's water flow to the medium setting or the maximum setting.
Some governments around the world set standards for water usage and regulate shower heads. For example, in the United States, residential and most commercial shower heads must flow no more than 9.5 liters per minute (2.5 gallons per minute) per the Department of Energy ruling 10 CFR 430. Low flow shower heads, less than or equal 7.6 liters per minute (2.0 gallon per minute), can use water more efficiently by aerating the water stream, altering nozzles through advanced flow principles or by high speed oscillation of the spray stream. USEPA administers a voluntary water saving program, WaterSense, which can certify low flow shower heads.
Meanwhile, how many liters are in 9 kav?
1 Kor (= 1 Chomer) = 30 Se'in 
1 Lesech = 15 Se'in 
1 Eifah = 3 Se'in 
1 Se'ah = 6 Kabin 
1 Tarkav (= 3 Kabin) = 12 Lugin 
1 Kav = 4 Lugin 
1 Log (= 1 Rova) = 4 Revi'iyos = 6 Beitzim 
1 Beitzah = 2 k'Zeisim 
1 k'Zayis = approximately 0.025, 0.0288 or 0.05 liters, depending upon the differing Halachic opinions. 
1 Kav = 4 Lugin = 24 Beitzim = 1.20, 1.38, or 2.4 liters, depending upon the differing Halachic opinions 

If so, taking the maximal 2.4 liters, multiply by 9, and 9 kav = 2.4 * 9 = 21.6 liters. Assuming a typical non-low-flow shower head at full blast, and it is a shower of 2.275 minutes.

However, that was assuming that a zayit was 0.05 liters. The minimal beitza is half that, 0.025 liters.

But then, according to Rabbi Slifkin in the Evolution of the Olive,
"An olive measures 4-6cc."
If we take the largest of those olives, and plug that into Google Calculator, we discover that:

1 olive = 6 (cubic centimeters) = 0.006 liters

We don't then automatically perform the calculations described above. Maybe a beitza is not really two kezeisim. Just to choose a more stringent definition to show how it might work out, Rabbenu Tam said that an olive must be less than 1/3 of an egg. So, let us adopt a stringent position that an egg = 4 olives, instead of 2 olives.

Since 1 kav = 24 beitzim = 96 kezeisim, then 1 kav = 96 x 0.006 liters = 0.576 liters
So, 9 kav = 9 x 0.576 = 5.184 liters.

Certainly, there is more than that in a 1 minute shower at full force.

If 1 kav = 24 beitzim = 48 kezeisim, then 9 kav would be half that.

Update: Please see correction from J. in the comment section. An egg is not to be related to an olive in any such manner.


  1. I think this is totally off. Rabbi Slifkin's whole point is that the Rishonim in Ashkenaz, who related the size of olives to eggs, had no idea what an olive was. So we can't use his (or anyone else's) measurements of contemporary olives to find out what a kav is. All we can do is measure eggs (which are around 50cc). Thus one log (six beitzim) is 300cc and one kav (four lugin) is 1200cc. Nine kabin is thus 10.8 liters. To get nine kabin at 5.184 liters, eggs would have to be around 25cc, which is simply untrue, and is never suggester by Rabbi Slifkin.

  2. I'm frankly amazed at R' Slifkin's position that the rabbonim of Ashkenaz didn't know how big an olive was. Some of them lived in France! Even the ones who lived in Germany had undoubtedly seen preserved olives at some point.

  3. Joe:
    why don't you ask Rabbi Slifkin?

    Good point. Thanks for the correction. I would point out, though, that he does mention the following: "My own research indicates that the eggs of ancient times were considerably smaller than those of today. Domestic fowl have been selectively bred for larger eggs, which would mean that eggs used to be smaller. Furthermore, we know that the domestic chicken was domesticated from the red junglefowl several thousand years ago, and its eggs are very small, only 32.1cc. Assuming a gradual increase to the size of today’s eggs, this would indicate that two thousand years ago, eggs were around 40cc. In addition, records show that the chickens used in Roman Italy were able to incubate twice as many eggs at a time than chickens of today are able to do, which shows that their eggs were much smaller.47""

    Even so, 32.1cc is a far cry from 25cc. I stand corrected, and will emend my text to note this.

    Thanks again,

  4. Since Tevilas Ezra is at most a derabbanan, and in fact is not even required acc. to most poskim, I would venture to say that one can rely on the more meikil view of shiurim if you want to fufill this chumra.

  5. Josh: I raised that point when R' Slifkin reposted his essay on shiurim a while ago, but he either didn't see it or didn't think it was worth rebutting. I don't have the patience to pursue it, but I think it's a pretty solid rebuttal to the idea that the Rishonim weren't aware of the discrepancies between various shiurim.

  6. Joe:

    Given that in the essay, he notes that Rishonim in Germany *explicitly* say that they are unfamiliar with the size of an olive, saying "Even the ones who lived in Germany had undoubtedly seen preserved olives at some point" is not necessarily an assumption one should make. (of course, one could teitch up any such statement.)

    i don't know about france, once an assumption exists in the halachic literature of your tradition, eyewitness observation does not necessarily help. all sorts of teirutzim such as that olives of different places are different or nishtaneh hateva then come into play.

  7. R' Slifkin says "We thus see that the Rishonim of Ashkenaz themselves acknowledged that, living in Ashkenaz, they had not seen olives." I'm disappointed by his tendency to make leaps from equivocal references. In this case, the best proof he has is Ravyah saying that he isn't familiar with the measurement of an olive. This sounds to me like he's commenting on the size of a kezayit, not the size of an olive, especially considering that Wikipedia says he travelled through France and Lombardy (Italy). I find it hard to imagine that nobody in Ashkenaz would think of buying preserved olives in the market, or asking one of their French or Italian students how big an olive is. I would certainly require a great deal more proof than R' Slifkin has presented.

  8. as i said, "one could teich up any such statement".

    i'd have to see context of the Rosh's statement, but it certainly does seem that he had to travel to Israel to see what an olive is, and once he saw it, he no longer had a difficulty. (one could of course teich up that statement as well.)

    in terms of France, "there is no mention of olive orchards until the 11th and 12th centuries... but the progression had to wait until the 17th century, a time in which olive cultivation and oil were becoming established in Provance", so perhaps it made this late an encroachment?

    I think you have not established that preserved olives are available in the market for this to be a strong question. Also I am not sure that they were driven by the same modern empirical spirit that drives you and me. did you learn through Yoreh Deah? if were you motivated, like me, to simply run an experiment to see if tataa gavar or ilaa gavar, rather than relying what was established as halacha?