Especially in the summer months, the question is frequently asked as to the permissibility of bathing or showering on Shabbat. May one take a shower on Shabbat if he feels uncomfortable or is perspiring, and, if so, what restrictions apply?
The first Halachic issue that must be addressed when approaching this issue is that of hot water. Because of the way our boilers work, turning on the hot water faucet would violate Shabbat, perhaps on the level of a Biblical violation. When one turns on the faucet and lets out hot water, cold water enters the boiler and becomes heated. The fact that one does not see this happening is irrelevant; the fact remains that turning on the hot water causes the heating of cold water, in violation of Shabbat. (It should be noted that this can often be a problem when one washes Netilat Yadayim in the sink. If the sink has one faucet with a lever, as opposed to separate faucets for hot and cold, and the lever is turned to the hot water, one must ensure to turn it to the cold water before turning it on, or else he could violate Shabbat by turning on the hot water. If the non-Jewish housekeeper had the hot water running, one may ask her to leave it running and then wash with the hot water, since the water was running already and he did not turn it on. In such a case one should leave the water running after washing Netilat Yadayim, as turning off the hot water may also entail Halachic problems.)
Clearly, then, it is forbidden to turn on the hot water to take a hot shower on Shabbat.
Furthermore, even if one is able to circumvent this problem, it is still forbidden to shower with warm water. The Sages enacted a prohibition forbidding washing the entirety or majority of one’s body with warm water on Shabbat, even if he did not heat the water on Shabbat. Thus, for example, if the housekeeper was washing the bathtub on Shabbat, one may not ask her to leave the water running and then take a hot shower. Likewise, if one has water in an urn, and he wants to fill a basin with hot water from the urn and wash with the warm water, this is forbidden. This is also one of the reasons why swimming is forbidden on Shabbat, as most pools today are heated. (There are also other reasons why swimming is not allowed on Shabbat, which do not relate to our discussion here.)
It is, however, permissible to wash one’s hands, face and feet with warm water, assuming, of course, that he does not warm the water on Shabbat. And thus one may fill a basin with hot water from the urn and use it to wash his face, hands and feet on Shabbat. And if the non-Jewish housekeeper had the hot water running, one may ask her to leave it on and then use it to wash his hands, face and feet.
If one wishes to take a cold shower on Shabbat, he may do so, according to Sephardic custom. (Ashkenazim act more stringently in this regard and refrain from even cold showers on Shabbat.) There are, however, several restrictions that apply. First, one may not squeeze water out of his hair or beard, as this would violate the Shabbat prohibition of Sehita (squeezing). Likewise, one may not use a washcloth or sponge, and one must ensure to use a large towel, as a small towel will become saturated and one will invariably squeeze water from it, in violation of Shabbat. Additionally, one should preferably avoid using bar soap on Shabbat (even though some authorities allowed using bar soap on Shabbat), and therefore one must use liquid soap. (Hacham Bension Abba Shaul held that even liquid soap should be watered down before being used on Shabbat.) Assuming one meets all these conditions, he may take a cold shower on Shabbat. This is the ruling of Rabbi Moshe Halevi (Israel, 1961-2001), in his work Menuhat Ahaba (listen to audio recording for precise citation).
Summary: It is forbidden to wash the entirety or majority of one’s body with warm water on Shabbat, even if the water was heated before Shabbat or by a non-Jew. One may wash his hands, feet and face with warm water, as long as a Jew did not heat the water on Shabbat. According to Sephardic custom, one may take a cold shower on Shabbat, as long as he does not squeeze water from his hair or beard, he does not use a washcloth or sponge, he uses liquid soap instead of bar soap, and he uses a large towel (as a small towel will become saturated and one will end up squeezing water from it).
