Is one allowed to take a hot shower or bath on Yom Tob?
When it comes to Shabbat, the Shulhan Aruch (Orah Haim 326) writes that the Sages enacted a law forbidding bathing on Shabbat even with water that had been heated before Shabbat. Such water may be used for washing one’s face, hands and feet, but not his entire body. Water heated on Shabbat may not be used at all, even for washing one’s face, hands and feet.
With regard to Yom Tob, however, the Poskim raise the possibility that there is greater room for leniency, in light of the fact that heating water is allowed on Yom Tob. As we know, cooking is allowed on Yom Tob, and the Sages extended the law permitting kindling a flame for cooking on Yom Tob to include kindling a flame for any purpose, as long as it is "Shaveh Le’chol Nefesh" – something that all people need, just like cooking. Thus, for example, under uncomfortably cold conditions, it is permissible to kindle a fire for heat on Yom Tob, as this is something which everybody needs. By the same token, then, one may heat water on Yom Tob to wash his face, hands and feet, as this was something which all people need. In ancient times, people were not accustomed to bathing their entire bodies each day, and so the Sages did not allow heating water for a full-body bath or shower on Yom Tob. Therefore, if one would want to heat water on Yom Tob for the purpose of bathing, he would be allowed to heat only the amount needed for his face, hands and feet.
However, there is some discussion as to whether there is greater room for leniency in our situation nowadays, where the water is heated automatically by the boilers in our homes. Although the water is heated on Yom Tob itself, nevertheless, the person does not actually heat the water; this happens on its own, through a process which was set in place before Yom Tob. This would appear to resemble the case addressed by the Magen Abraham (Rav Abraham Gombiner, 1633-1683), in Siman 326, of a stream of cold water which passes through a pool of hot water, thereby becoming heated. The Magen Abraham allows using this heated water on Shabbat to wash one’s face, hands and feet, even though it was heated on Shabbat. Rabbi Akiva Eiger (1761-1837) explained that since no human action on Shabbat is involved in heating the water, this situation is akin to one of water which is heated before Shabbat, such that it may be used for washing one’s hands, feet and face.
Hacham Ovadia Yosef applied Rabbi Akiva Eiger’s line of reasoning to the case of a "Dud Shemesh" – solar-powered boilers, which are very common in Israel. Even though the water is heated on Shabbat, nevertheless, since there is no human involvement in the process of the water’s becoming heated on Shabbat, this water may be used. Therefore, Hacham Ovadia writes, on Yom Tob, it is permissible to bathe one’s entire body with hot water from the solar-powered boiler.
Hacham Ovadia acknowledges that some might question his lenient ruling in light of the fact that when one opens the faucet to let out hot water, cold water enters the boiler and is heated. This water is not heated for any need which one has on Yom Tob, and thus causing this water to be heated would, at first glance, seem to be forbidden on Yom Tob. However, Hacham Ovadia refutes this argument, explaining that since one has no intention to heat this water, and heating it on Yom Tob is forbidden only Mi’de’rabbanan (by force of Rabbinic enactment, as opposed to Torah law), one may open the faucet even though he will end up heating the new water that enters the boiler.
Hacham Bension Abba Shaul (Israel, 1924-1998) disagrees with this lenient ruling. He does not accept Rabbi Akiva Eiger’s rationale permitting the use of water which was heated on its own on Shabbat, and so in his view, full-body showers are forbidden on Yom Tob even from a solar-powered boiler.
Rav Yisrael Bitan, in the English edition of Yalkut Yosef, writes that fundamentally, the case of our electric boilers, which are turned on at all times, should be no different from the situation of the solar-powered boilers addressed by Hacham Ovadia. It stands to reason, then, that showering and bathing normally on Yom Tob would be allowed, since no human action is involved in heating the water on Yom Tob, as the system was set into place before Yom Tob. Nevertheless, Rav Bitan stops short of actually allowing full-body bathing on Yom Tob, since Hacham Ovadia did not explicitly extend his ruling to electric boilers.
In practice, it would appear that those who experience considerable discomfort without showering on Yom Tob may rely on Hacham Ovadia’s ruling. (In fact, Rabbi Akiva Eiger rules that those who find it uncomfortable not to bathe may do so even on Shabbat if the water was heated before Shabbat.) Infants and young children, too, may be bathed normally with hot water on Yom Tob if necessary. Others, however, should refrain from showering with hot water on Yom Tob, but they may, if they wish, bathe with lukewarm water, which is certainly allowed.
Summary: Those who experience considerable discomfort without a hot shower or bath on Yom Tob may take one. Likewise, infants and young children may be bathed with hot water on Yom Tob if necessary. Otherwise, one may wash his hands, feet and face in hot water, or wash his entire body in lukewarm water.