If a Mikveh is not available:
The immersion in a Kosher Mikveh accomplishes two matters. It purifies a person from the Keri impurity and it adds extra purity to the soul, cleansing it in a form of Teshuvah [i.e. Tosefes Taharah]. According to many Poskim these two aspects and benefits are independent of each other and receive separate laws in a case that a Kosher Mikveh is not available. Regarding the purification from Keri the Sages established that a Kosher Mikveh is not required and hence the immersion in drawn water or pouring of nine Kavim is valid, [as will be explained below]. However regarding the purity added to the soul these forms of Mikveh are invalid. Hence one is always to prefer a Kosher Mikveh over using the methods below and the methods below are to only be used when there is lack of alternative. On the other hand there is also a stringency regarding the purification of a Baal Keri over the aspect of Tosefes Taharah, as the Poskim bring that in a time of need one may pour water over the hands or learn Mishnayos to accomplish the Tosefes Taharah. It however does not help to purify one from the state of Keri. [See Q&A for details on this topic]
Using Mayim Sheuvim-swimming pool: To achieve purification from the state of Keri one may immerse in 40 Seah [90 gallons or 332 liters] of even drawn water that is in the ground [such as a typical swimming pool]. However it does not help to immerse in a vessel that contains drawn water.
Nine Kavim-shower: If one is not able to immerse in any body of water [even a swimming pool and the like] then he is to pour nine Kavim [12.5 Liters] of water over his body. One may use up to 2 or 3 buckets of water for this purpose, pouring each bucket one after the other, if in total they contain nine Kavim of water. In such a case one must begin pouring the second bucket prior to finishing the pouring of the first bucket, and so too one must begin pouring the third bucket prior to finishing the pouring of the second bucket. It is invalid to use four buckets of water for the accumulation of nine Kavim, [and hence if the first three buckets or last three buckets do not contain nine Kavim in total it is invalid]. Even when pouring from one vessel one must be careful that the water continuously falls on him without any interval at all. If one entered halfway into a Mikveh and on his top half he poured nine Kavim, it is valid. [See Q&A regarding shower]
If it is painful for one to immerse in the Mikveh or he is sick: If it is painful for one to immerse in a Mikveh [such as the water is too cold, or one is sick] then he may follow the method brought above of pouring nine Kavim of water. [However one should not initially choose pouring nine Kavim over immersing in a Mikveh as the nine Kavim only accomplish the removal of the Keri impurity. It however does not accomplish the additional purity added by immersing in a Mikveh.]
Washing the hands forty times in a case that one is unable to immerse in a Mikveh or shower: See Q&A!
Q&A on Sheuvim
Can one fill up his bathtub and immerse in the water for purification of Keri?
It is only valid to do so if: a) the hole of the bathtub is at least 3.8 centimeters wide, and b) one is able to stop up the hole, and c) it is filled with 332 liter of water, and d) one is able to fully immerse his entire body within the water simultaneously. [Typical bathtubs are not large enough to accomplish this by a normal sized person.]
Q&A on Nine Kavim
Can one perform “nine Kavim” in the shower?
Yes. One can do so by staying under the shower head for 3-4 minutes consecutively without turning the water off for even a moment in between. One is to stand straight under the shower head with his hands weakly folded over his chest as explained next. It is invalid when one is lying in the bath, as will be explained.
How is the nine Kavim to be poured over the body?
The water must be poured over the entire body. One is to stand straight with his hands weakly folded over his chest or along his sides down to the thigh and have the water poured directly over his head. It is not necessary that the water actually touch every part of the body. Nevertheless some Poskim rule that one is to wet his feet beforehand in order so the water being poured attaches to the water under his feet. It however does not have to touch the armpit and the like. It is not valid if the water was poured only on one part of the body even if one later pours on the other part. However there are Poskim that are lenient in such a case.
Does a Chatzitza/interval invalidate the nine Kavim?
One must remove all intervals from the body prior to pouring the nine Kavim.
Does it help to immerse in nine Kavim?
No. The nine Kavim are only valid if they are poured onto the person and not when one immerses in them. This applies whether the water is in the ground or in a vessel. If however it contains 40 Seah in the ground then it is valid for immersion.
Lying in a bath and having the nine Kavim [shower] poured over his body:
The nine Kavim are only valid if they are poured over his entire body, as stated above. Thus it is invalid for one to sit or lie in a bathtub with water and have the nine Kavim poured over his head.
Other alternatives to a Mikveh
Washing the hands forty times in a case that one is unable to immerse in a Mikveh or shower:
If one is unable to immerse in a Mikveh or shower with nine Kavim then he should purify his hands by pouring water on them forty times. The order is as follows: One first pours ten times on each hand, alternating between each hand after each pour. One then pours ten times consecutively on the right hand and ten times consecutively on the left hand for a total of 40 pours between the two hands combined. The 40 acts of pouring correspond to the 40 Seah of a Mikveh. One is to intend the Divine 72 letter name [שם ע“ב], which is found in the Divine name of Havaya, during these pourings. [The Rebbe states that these pouring only give a person the additional purity that the immersing in a Mikveh accomplishes, however it does not remove the Keri impurity from the body.]
One who is unable to immerse in a Mikveh is to learn Mishnayos that deal with the laws of Purity. This especially applies to Miseches Mikvaos. Nevertheless this only give a person the additional purity that the immersing in a Mikveh accomplishes, however it does not remove the state of Keri impurity from the body.
If one immersed in a pool or performed nine Kavim should he also pour forty times on his hands or recite the Mishnayos?
Seemingly one is to do so in order to gain the additional purity received from these washings. However we have not seen this witnessed.
 606/11 regarding Erev Yom Kippur
 Shalah Hakadosh Yuma p. 288; Minchas Yitzchak 3/64; Kinyan Torah 1/33; See Igros Kodesh 9/353; Igros Kodesh brought in Shulchan Menachem 1/143; Igros Kodesh Rebbe Rayatz 2/142 distinguishes between the two matters regarding pouring and Mishnayos.
 Shalah; Minchas Yitzchak; Kinyan Torah brought in previous footnote.
Other Poskim: Some Poskim are lenient and rule that the leniencies of Sheuvim [and Zochlin] apply even when one immerses for Teshuvah or Tosefes Taharah. [Munkatcher in Divrei Torah 9/83; Torah Leshma 375; Piskeiy Teshuvos 88/6] Nevertheless even the above Poskim are initially stringent [Darkei Chaim Veshalom 356; Piskeiy Teshuvos ibid]
 Shalah ibid; Minchas Yitzchak ibid; Kinyan Torah ibid
 Kinyan Torah 1/33; Piskeiy Teshuvos 88/4; and so is implied from Admur 606/11-see previous footnotes.
 606/11; 88/1
 Shiurei Torah 3/29
Other Opinions: According to the Chazon Ish 40 Seah is 576 liters.
 As this immersion for the purpose of purifying oneself from the state of Keri is valid even when using drawn water. [ibid]
 606/11; 88/1 [in parentheses]; M”B in name of Rav Akiva Eiger; Stringent opinion in Gemara Brachos 22b; See Piskeiy Teshuvos 88 footnote 44 for a discussion on this matter.
Other Opinions: There is an opinion in the Gemara ibid that rules a vessel is valid for a Baal Keri.
 88/1; 606/11; Taz 88/1; Olas Tamid 88/2; M”A 606/9; Elya Raba 606/11
 Shiurei Torah 3/30 writes that 9 Kavim is equivalent to 12.441 liters of water. The Piskeiy Teshuvos 88/5 writes that according to the Grach Naah [author of Shiurei Torah] one is to initially use 18 liters and 12.5 litters is only in a time of need. Vetzaruch Iyun as to his source, being that the Grach Naah explicitly writes 12.5 liters.
Other Opinions: The Chazon Ish rules that initially it is to be 23 liters and in a time of need 17.5 liters suffice. Others rule it is 11.3 liters. [brought in Piskeiy Teshuvos ibid] Others rule it is 16 Liters. [Minchas Yitzchak 4/51]
 Admur ibid; Some Poskim [Bier Heiytiv 88] record 3-4 buckets are valid. This is a printing error. [Kaf Hachaim 88/6]
 606/11 regarding Erev Yom Kippur; However in 88/1 Admur plainly rules that a Baal Keri can even initially perform nine Kavim and does not limit this to one who is sick. Seemingly the reason is because everyone agrees that nine Kavim remove the Keri impurity however it does not purify a person like a Mikveh for purposes of Teshuvah, and since some opinions rule one immerses Erev Rosh Hashanah and Erev Yom Kippur for purposes of Teshuvah, it is only to be used as a last resort. [See Kinyan Torah 1/33]
 M”B 581/26
 Kinyan Torah 1/33; Piskeiy Teshuvos 88/4; and so is implied from Admur 606/11-see previous footnotes.
 Divrei Yichezkal 13; Piskeiy Teshuvos 88 footnote 44
 Shiurei Mikveh p. 163 [However Lechatchila it is to be 4.8 cm wide]
The reason: This is the measurement required for an item to not be considered a vessel.
Other Opinions: According to the Chazon Ish Shefoferes Hanod is 4.8 cm wide.
 Kinyan Torah 1/33; Tzur Yaakov 9; Chelkas Yaakov 3/61 Minchas Yitzchak 4/51; Vayaan Yosef 1/45; Divrei Yaatziv Likkut 13; Beir Moshe 6/74; Shraga Hameir 1/16; Sheivet Halevi 1/24; Piskeiy Teshuvos 88/5
Other Opinions: Some Poskim are stringent and disqualify the use of a shower on the basis that according to the Raavad one requires Koach Gavra to validate the nine Kavim. [Opinion of Mishneh Halachos 3/2-6; 3/8; 5/19-22; 6/23]. The vast majority of Gedolei HaPoskim ibid however rule it is allowed based on that we do not rule like the Raavad in this matter, and even according to the Raavad today that the nine Kavim is only a custom he would agree it is allowed. [Kinyan Torah ibid]
 Piskeiy Teshuvos 88 footnote 42 [This applies even according to the opinion that requires 23 liters]
 M”B 88/4; M”E 606/10; Kaf Hachaim 88/7
 So is implied from Mateh Efraim ibid; M”B ibid that state “Neged Libo” and that it should not be “a forceful hug”.
 Kaf Hachaim 88/7
 Alef Lamateh 606/3; However see P”M 88 M”Z 1 that learns from the Rambam that the water must touch every area of the body. Nevertheless the P”M himself concludes that the custom is not to do so. See Eretz Tzvi 1/89; Shaareiy Teshuvah 88/1 in name of Mamar Mordechai
 P”M 88 M”Z; Kaf Hachaim 88/7
 Piskeiy Teshuvos 88/5, and so is proven from the P”M ibid which does not require to wet it beforehand.
 Beir Moshe 5/18
 Rav Shlomo Kluger in Shiyurei Taharah brought in Piskeiy Teshuvos 88/5 footnote 38
 Alef Lamateh 606/3; Eretz Tzvi 1/89; Piskeiy Teshuvos 88/5
 Admur 88/1; M”B 88/4 in name of Beis Yosef; Piskeiy Teshuvos 88/5
 Mateh Efraim 606/12; Unlike ruling of Divreiy Yisrael 1/11 brought in Piskeiy Teshuvos 88 footnote 40
 This is unlike the case stated in Admur ibid that it is valid to pour the nine Kavim on the upper part of the body when the lower part is in the Mikveh, as that law only applies by a Kosher Mikveh and not to the water in a bathtub. [M”E ibid]
 Ben Ish Chaiy Netzavim 3 based on Sefer Emes Leyaakov; Kaf Hachaim 76/22; Ashel Avraham Butchach 88; Rav Mottle Chernobyl brought in Sefer Chesed Leavraham; Piskeiy Teshuvos 88/4; Igros Kodesh 9/353
 Thus the first pour is on the right hand, the second on the left, the third on the right etc until by the 20th pour each hand received ten pours inconsecutively.
 See Kaf Hachaim ibid; Piskeiy Teshuvos 88 footnote 31
 The following is the Kavana: The name Havaya when written in full [with the unseen pronounced letters] contains 10 letters (יו“ד–ה“י–וי“ו–ה“י). These ten letters equal the Gematria of 72. Prior to beginning the pouring one is to supplicate to G-d and say “May it be Your will that this washing of the hands be considered as if I immersed in 40 Seah of a Mikveh….. “ One is then to pour on the right hand one time intending the first letter “Yud” he then pours on the left hand one time also intending the first letter “Yud”. He continues intending each letter for each pouring of right-left for a total of ten letters, each letter being intended by each set of right left pourings. He is then to pour ten times consecutively on the right hand intending one letter of the Divine name by each pouring. He then repeats this order for the left hand. [Emes Leyaakov brought in Kaf Hachaim ibid]
 Igros Kodesh 9/353
 Igros Kodesh brought in Shulchan Menachem 1/143; Igros Kodesh Rebbe Rayatz 2/142
 As explained above that the Nine Kavim or Mayim Sheuvim only help to remove the Keri impurity and not for Tosefes Taharah which is accomplished through a Mikveh.