It is forbidden to wash your entire body, or even most of your body with hot water, even if it was heated on Friday.¹ Even to wash one limb at a time, is forbidden when the majority of the body [will be washed]. Even to enter a bathhouse solely for the purpose of sweating is also forbidden. But you may wash your face, hands and feet² 326: 1] with hot water that was heated on Friday.³] Others disagree. [Minchas Shabbos, Tehilla Ledavid, Magein Avraham 261: 12]

footnotes: ¹ This is a Rabbinic prohibition, lest you heat the water on Shabbos. ² Or any limbs, provided they do not constitute most of the body. [v. Rema ³ If you experience great discomfort, some rule that you may bathe in water heated Friday. [Biur Halachah, Rabbi Akiva Eiger

Water that flows hot from its source such as the hot springs of Tiberias and the like, if [the waters] are in the ground and there is no roof over them, you may wash even your entire body⁴ 40] in them. But, if [the water] is in a vessel⁵ or the place is covered with a roof, it is forbidden.⁶ (sauna room) which may not be used on Shabbos. The Mishnah Berurah, however, (citing Shulchan Aruch 326: 22) rules that you may use heat from hot springs for sweating since even bathing is permitted there. Even to enter a bathhouse solely for the purpose of sweating, is forbidden.⁷ (326: 12). However, Rema (from Rashi and Tur) rules that even just passing through without intention to sweat is prohibited. There are those who say that as long as [the water] is in the ground even if the place has a roof, you may bathe in it.

footnotes: ⁴ Only water heated by fire is prohibited. [Maseches Shabbos ⁵ In such a case, the hot water may be confused with water heated by fire. ⁶ The roof increases the heat of the room, making it akin to a “shvitz” ⁷ Because some who are unscrupulous may go to bathe and claim that they are going only to sweat.The words of the author imply that merely passing through a bathhouse is permitted which is the opinion of Shulchan Aruch

You may immerse your entire body in cold water.⁸ 326: 21 from Magein Avraham and poskim] V. paragraph 4. Some poskim, however, do permit immersing in a warm mikveh on Shabbos. However, you may not stand afterwards in front of an oven in order to warm yourself, because that amounts to washing in hot water. Even if you washed only your hands in cold water, do not warm them near the oven while they are still wet, because it is considered as if you washed with water that was warmed today [Shabbos], for such water is prohibited for washing even one limb.⁹] You must first dry them well and as stated in Chapter 80, paragraph 32, you must rub them well before drying them so that only a little water remains on them.

footnotes: ⁸ It is customary not to wash even in cold water so as not to squeeze the water from your hair. [Mishnah Berurah ⁹ Even if the water is only lukewarm. [Mishnah Berurah

If you bathe, be careful not to squeeze your hair.¹⁰ prohibition, since you have no need for the water squeezed from the hair. [Mishnah Berurah 326: 25–28, see also Igros Moshe o.c. 133] Drying the hair is also permitted. [v. Minchas Shabbos] Avnei Neizer (o.c. 157) rules not to wash hair with your hands lest you inadvertently pull out some hairs. [v. Shemiras Shabbos Kehilchasah, Ketzos Hashulchan] Also take care not to swim because it is prohibited to swim on Shabbos and Yom Tov.¹¹ 36, Shulchan Aruch 339: 1] The author later writes that it is the custom not to bathe in an ocean or pool even without swimming. [v. Mishnah Berurah 326: 21] It is also forbidden to make things float, such as wood chips, on top of the water.¹² 339: 6] This prohibition applies only in a river, lake or ocean, but in a tub or pool it is permitted. [Bach, Magein Avraham, Mishnah Berurah] If you bathe in a place where it is forbidden to carry, you must also take care before leaving [the water], to first remove the water from your body and hair, and dry yourself well, so that no water remains on you, which you would be carrying from one domain into another.¹³ 141] Similarly, care must be taken not to carry the water four amos in a karmelis. [Shulchan Aruch 326: 7] Similarly, in the river itself, you must take care not to carry the water which is on you four amos, because the river is considered a karmelis.¹⁴ 326: 22. Some argue that the Shulchan Aruch does not agree and allows walking within the river because the water on your body is considered one with the water in the river and is not considered as being carried from one place to another. [Minchas Pittim] Also, your intent while walking is not to carry the water and is, therefore, permitted. Also, the amount on your body is negligible (less than a revi’is) which Meiri permits even out of the water. [Eretz Tzvi 72] Since not everyone knows to be careful, therefore, it has become the prevailing custom in these regions not to bathe at all on Shabbos even in cold water, except for the purpose of a mitzvah, such as a woman after menstruation, (as discussed further, Chapter 162, paragraph 7) or a man after a nocturnal emission.

footnotes: ¹⁰ Washing itself is permitted because squeezing water from the hair is only a derabanan ¹¹ [Maseches Beitzah ¹² [Yerushalmi, Shulchan Aruch ¹³ [Maseches Shabbos ¹⁴ Peri Megadim, Mishnah Berurah

You may stand at the river bank and wash your hands in the river; and it is not forbidden to remove the water on your hands from the river onto the bank, because the river is [considered] a karmelis and the bank is also a karmelis, and it is permitted to carry from one karmelis to another less than four amos, provided that you take care to dry your hands thoroughly before walking four amos.

You may clean your hands by rubbing them with crushed grain [or bran] although your hands may be wet,¹⁵ provided you don't put the water directly on the crushed grain. But it is forbidden to rub your wet hands with salt, and, certainly, not with soap because it liquefies.¹⁶). [Rema 326: 10] The Mishnah Berurah adds that the author is referring to very hard soap and it is, therefore, only a derabanan prohibition. Use of our softer soaps would be a de’oraisa prohibition of מְמַחֵק (smoothing). [Mishnah Berurah 326: 30, Tiferes Yisrael]

footnotes: ¹⁵ This does not constitute לִישָׁה (kneading) because: 1) it is not the usual manner of kneading, and 2) it is not your intent to knead. ¹⁶ And takes on a new form. This constitutes the prohibition of נוֹלַד (nolad

Water that is not usually used for washing, but, rather, for medicinal purposes, such as malodorous or noxious [water], is forbidden to be used for washing on Shabbos, since it is obvious that it is being used as a cure, (see below, Chapter 91).¹⁷ This applies only if you linger in [the water], but, if you do not linger, it is permissible, because [then] it appears [that your purpose is] only to cool off.¹⁸ 328: 44. Concerning the hot springs of Tiberias and the like: if the normal practice is to bathe in them only for health reasons, it is forbidden to bathe in them on Shabbos for health reasons, even if you do not linger in them.¹⁹ 328: 140]

footnotes: ¹⁷ The laws concerning medicine are discussed there. ¹⁸ Shulchan Aruch ¹⁹ The prohibition applies only where the purpose of the bath is only to alleviate slight discomfort. When one is actually ill (even where no danger is involved) he may bathe in the hot springs. [Mishnah Berurah