For six days labor may be done, and the seventh day is a day of complete rest, a holy convocation, you shall not do any work; it is a Sabbath for Hashem in all your dwelling places. (Vayikra 23:3)
One of the most basic practices of medical personnel working with patients with highly infectious diseases, including COVID-19, is to thoroughly disinfect themselves at the conclusion of their shifts, including showering. Despite the use of full personal protective equipment (PPE) – including gowns, masks, faceshields, and gloves – there is still a grave concern of infection due to exposure to sick patients. Showering with hot water ensures complete disinfection.
This raises the question of whether it is permissible to take a shower on Shabbos following a shift. Rechitza (showering or bathing) on Shabbos is forbidden in many cases. But is it an Issur d’Rabbanan or d’Oraisa? If the person in question is young and healthy who may not be particularly endangered by infection, is taking a shower still a matter of Pikuach Nefesh? Should we consider that he may spread the disease to others, many of whom are at high risk of complications?
One of the 39 Melachos of Shabbos is Bishul (cooking). In the Mishkan, various herbs and plants were cooked to produce the dyes that were used for the tapestries, and Bigdei Kehuna. However, even boiling water is also included in the Melacha, as the Rambam rules in Hilchos Shabbos (9:1).
Therefore, the Halacha in this matter largely depends on the manner of heating the water. Hospitals in Israel generally employ systems that do not cause Chilul Shabbos by ensuring that the water does not reach a temperature that is defined in Halacha as cooking. Heating water to a temperature below the definition of Bishul is termed “Hafshara” which is permissible on Shabbos (Shabbos 41b).
Bishul only occurs when something reaches the stage of “Yad Soledes Bo” – when a person touching it would withdraw his hand due to the heat. When an item reaches Yad Soledes Bo, it is considered to be “Rosachas” (very hot), but the precise temperature at which it reaches this stage is a matter of dispute. Rav Shlomo Zalman Auerbach zt”l based his estimation on the Gemara in Chulin (8b) which asserts that the “Beis haShechita” – the area of an animal’s neck that is cut during Shechita, is only “Roseiach” after the Shechita. The body temperature of slaughtered animals is equivalent to that of febrile pigeons or turtle-doves, which is as high as 47 degrees. This means that any temperature below that is not considered “Roseiach”, so this should also be the definition of Yad Soledes Bo.
There are more stringent opinions as to the temperature of Yad Soledes Bo, and in order to satisfy all opinions, hospitals in Israel set the maximum temperature in their hot water heaters to a temperature that is certainly not Yad Soledes Bo. (In Shaare Zedek Medical Center the thermostat is set at 43 degrees, and in Mayanei Hayeshua Medical Center in Bnei Brak it is set at 40 degrees, according to the ruling of Rav Shmuel Wosner zt”l).
While this may resolve the issue of Bishul, there is still an Issur of Rechitza to contend with. Chaza”l forbade Rechitza of the entire body on Shabbos, even if one uses water that was heated on Erev Shabbos, and they also forbade Rechitza of even a single area of the body if the water was heated on Shabbos itself. The Gemara (Shabbos 40b) explains that this enactment came about on account of bathhouse owners who would heat up water on Shabbos (thus violating the Melachos of Hav’ara – lighting a fire – and Bishul) and claim that they had heated it before Shabbos. The Chachamim therefore completely forbade Rechitza with hot water.
The Shulchan Aruch (326:1) rules:
It is forbidden for a person to wash his entire body, even one limb at a time, even with water that was heated up before Shabbos… But it is permitted to bathe one’s whole body in the hot springs of T’verya, and it needn’t be said that one may bathe in cold water.
The Shulchan Aruch clearly states that bathing in cold water is permitted. However, there is a dispute among the Poskim at to whether bathing in hot water that is cooler than Yad Soledes Bo is permitted. Some hold that the Issur of Rechitza is equivalent to the Issur of Bishul and is only forbidden when the water is at a temperature of Yad Soledes Bo. Others say that the Chachamim forbade Rechitza if the water is at a comfortable temperature, even if it is cooler than Yad Soledes Bo. Contemporary Poskim rule stringently in this matter given that it is unusual for a person to bathe in water that is Yad Soledes Bo and it is likely that the Chachamim forbade bathing in water which people are accustomed to bathing.
Nevertheless, haGaon Rav Asher Weiss Shlit”a (in his new Kuntres about the Coronavirus outbreak, Teshuvos Ketzaros p. 47) ruled that medical personnel may be lenient in this matter as it is a Sha’as ha’Dechak and perhaps even a matter of Pikuach Nefesh. R’ Akiva Eiger (Hagahos O.C. 326:1) ruled that a “Mitztaer” (a person severely discomforted by not bathing) may bathe on Shabbos, even though he is not considered significantly ill, and may even use hot water that was heated on Erev Shabbos (ibid. 307:5). Our case is no less a Sha’as ha’Dechak.
Additionally, if they shower in lukewarm water, there is no Issur of Rechitza involved at all as outlined above. Although the Maharil and Terumas haDeshen (and later the Magen Avraham 326:8 and Mishna Berura ibid. 21) maintain that the Minhag is to refrain from Rechitza even in cold water, one may certainly be lenient in these circumstances.
This would only apply in a hospital (or other scenario) where the maximum water temperature is set below Yad Soledes Bo. Turning to the issue of showering at home on Shabbos, we will discuss the questions of Bishul that arise and some possible solutions.
In Israel it is common to heat water using a “Dud Shemesh” – a tank of water that is heated by solar panels. The question is whether one may one use hot water from a Dud Shemesh on Shabbos. This question was discussed by many of the Poskim of the past century.
The Gemara (Shabbos 39a) rules that one may cook something in the heat of the sun on Shabbos because doing so isn’t a regular method of cooking. Nevertheless, it is Assur mi’d’Rabbanan to cook by means of “Toldos haChama” (in other words, cooking using the heat of an item that was itself heated up by the sun). Therefore, while one may heat water directly in the sun, he may not heat cold water by mixing it with hot water that had been heated by the sun.
The reason that the Chachamim forbade Toldos haChama is that it is impossible to discern whether an item was heated up by fire or by the sun. Therefore, if we were to permit cooking by means of Toldos haChama people would mistakenly conclude that one may similarly cook by means of something that was heated up on the fire, which is forbidden.
A Dud Shemesh is a direct solar water heating system in which a supply pipe fills the tank with cold water. A second pipe (at the bottom of the tank) feeds the water into pipes adjacent to the solar panels. As the water in those pipes is heated by the sun, the less dense hot water rises to the upper area of the panel and back into the top of the tank via another pipe. This then displaces cold water in the tank into the pipes adjacent to the solar panels which will similarly be heated up. This cycle repeats itself until all of the water in the system reaches the same temperature.
When opening a faucet in the house, some of the hot water is siphoned off through a pipe from the upper section of the tank, and cold water then enters the tank to replace it. The cold water will settle at the bottom of the tank and the hot water (which is less dense) will remain at the top.
We have already noted that cooking on Shabbos using Toldos haChama is an Issur d’Rabbanan. Using the water from a Dud Shemesh would seem to cause Bishul by Toldos haChama, as it causes cold water to enter the system and be heated up by the hot water that is already present (which is Toldos haChama). This would seem to be a strong reason to prohibit its usage. On the other hand, it is often the case that one has already used a significant amount of the hot water on Erev Shabbos. Therefore cold water has already been fed into the tank to replace the hot water and has not yet been heated. Thereafter, any further cold water which enters the tank is unlikely to be heated up by the remaining hot water in the tank, so there is no Bishul by Toldos haChama (and if Bishul does occur it would be considered a Davar She’eino Mischavein and permitted Lechatchila).
Nevertheless some Poskim still forbid it, for even if the water won’t be heated up when it first enters the tank, it will be heated up at some point over Shabbos. However, other Poskim permitted it and in the case of medical personnel it would seem reasonable to take a lenient position. Moreover, since this is at most an Issur d’Rabbanan, there is room to consider their circumstances as a “Makom Choli” – a case of sickness in which one may override Issurei d’Rabbanan, even if one is usually stringent in this matter.[Furthermore, if the person in question is taking a shower on Friday night when the sun isn’t shining, the water that enters the tank will certainly not be heated up until the following day. This means that opening the faucet was no more than a Grama (an indirect cause), which according to Rav Shlomo Zalman Auerbach zt”l (cited in Shemiras Shabbos Kehilchasa) is permissible.]
Homes that are not equipped with a Dud Shemesh often use an electric boiler system that is regulated by a thermostat. If a person will need to shower on Shabbos, they should disable the boiler before Shabbos so that it won’t be activated when they use the hot water. As for the concern that the cold water entering the boiler will be heated up by the hot water that is already there – one can safely assume that the water at the bottom of the boiler isn’t hot enough to heat the cold water coming in to Yad Soledes Bo. Certainly, if one empties some of the hot water boiler before Shabbos there is very little chance that Bishul could take place when the cold water enters the boiler. Furthermore, when using the hot water to shower, one should be careful to only mix it with a volume of cold water that will not be heated to Yad Soledes Bo or use only hot water.
Another alternative is to adjust the thermostat to lower than 45 degrees – i.e. lower than Yad Soledes Bo – so that no Bishul will occur. Though using the hot water may still cause activation of the heating element in the boiler (as the new cold water will lower the temperature in the tank below the thermostat setpoint), it is both a Davar She’eino Mischavein and a Grama. Even if the person suspects that the temperature of the water is such that the boiler will be immediately activated as soon as he opens the faucet, it is still not a Psik Reisha.
None of these suggestions are applicable in the case of a tankless water heater or gas boiler that is immediately ignited when a person opens the faucet. Furthermore, in Chutz la’Aretz it isn’t always possible to ascertain which type of system a hospitals employs to heat its water, and one certainly will not be able to adjust the thermostats or make any other plans to avoid Bishul of the water.
In these circumstances, the best option would be to ask a non-Jew to turn on the water, shower without adjusting the faucets at all, and ask the non-Jew to close the faucet when he finishes. If that isn’t a reasonable solution, he should open and close the faucets with a Shinui (such as with his foot or the back of his hand). Even though a Shinui has no effect upon the ignition of the boiler or the heating of the water, in Hilchos Shabbos a Shinui is considered in relation to the person performing the act – if he does it in an unusual manner, it is a Shinui, even if the outcome of his act is identical as if he had done it in the normal fashion.
Additionally, since the concern in this case is about an infectious disease, one is justified in desecrating Shabbos given the grave danger to the public at large. The Chazon Ish (Oholos 22:32) rules that whenever a plague or pandemic are present, even a slight possibility of danger constitutes an outright Sakana. Therefore, although the risk to his own life is slight, a person may shower after his shift, even if he must rely on utilizing a Shinui to permit it, in order to prevent him from spreading the disease to others.
Furthermore, Rav Yehoshua Neuwirth zt”l (in the Sefer Torah sheBa’al Peh 9) raises many doubts regarding the Issur of using a boiler and thermostat on Shabbos. Therefore, there is certainly room to be lenient and utilize a Shinui to activate a boiler.[Approximately one hundred years ago, with the advent of central heating, the question of removing water from a heating system on Shabbos was discussed by Rabbis studying in the “Beis haMedrash l’Rabbanim” in Germany. They concluded that doing so did not directly introduce cold water into the system, nor was there a Psik Reisha that the system would be activated when hot water was removed. Moreover, the systems sometimes involved a heat exchanger which is considered to be a Kli Sheni in which Bishul is impossible.]
Regardless, when taking a shower, a person should ensure that he doesn’t inadvertently violate other Halachos of Shabbos such as squeezing water out of his hair or out of a towel, and he should also use liquid soap and not bar soap.
 The Gemara is discussing whether an animal slaughtered with a nonkosher knife is considered to have absorbed any of the nonkosher absorptions (B’lios) in the knife (which only occurs at or above the temperature of Yad Soledes Bo), and concludes that although the Beis haShechita is considered Roseiach, that is only after the Shechita and not at the time the knife is in contact with the animal’s blood.
 For example, Rav Moshe Feinstein zt”l (Igros Moshe O.C. 4:74).
 See the Shu”t Chelkas Yaakov (125). The Sefer Sh’eilas Shlomo (1, p114) relates that R’ Yehoshua Neuwirth zt”l also permitted this as the modern design prevents direct mixture of the hot and cold water.
 See the Orchos Shabbos, 1:120
 Rav Shlomo Zalman Auerbach zt”l