Hot Water That Was Re-boiled on Shabbos

Published: June 15, 2026 Reading time: 6 minutes

Does Bishul Apply to Water?

Bishul is one of the 39 forbidden melachos on Shabbos. The Gemara¹ defines the melacha of cooking as transforming a substance through heat produced by fire, whether by making something edible, hardening it, or softening it.

Although cooking water doesn’t seem to change it in any way, it is still clear in the Poskim that cooking water on Shabbos is assur min haTorah.² The Mishnah Berurah³ explains the reason: Water is improved when heated, because a warm drink is considered more choshuv. Cold water is generally consumed simply to quench thirst and does not carry the same significance, whereas warm water, which is usually used for tea or coffee, is considered a more distinguished beverage.

Bishul Achar Bishul

Although cooking water on Shabbos is forbidden, in our case the water had already been cooked before Shabbos, and the urn turned off after the water had already been fully heated. Can something that was already cooked be cooked a second time?

The Mishnah⁴ states that “ein bishul achar bishul,” meaning that something which was already cooked will not cook again.

Rashi and others⁵ explain that this rule applies only to dry foods: once they have been fully cooked, there is no further prohibition of cooking them again. Liquids⁶, however, retain an issur bishul even after having been previously cooked. Other Rishonim⁷ maintain that this rule applies to all foods, whether solid or liquid.

The Shulchan Oruch⁸ paskens that once the liquid cools down even a bit, we say “yeish bishul achar bishul.” The Rema⁹, however, appears to hold that reheating a liquid is only prohibited once it has completely cooled off. If it retains some warmth, reheating it is permitted min haTorah.

The Shulchan Oruch HaRav¹⁰ accepts the Rema’s ruling that if the liquid is still somewhat warm, even below yad soledes bo, it may be reheated.¹¹ The Mishnah Berurah¹² rules similarly. According to the Shulchan Oruch HaRav, the definition of “still warm” is that the food or drink remains fit to be eaten or consumed in its current state of warmth.

There is discussion among contemporary Poskim whether the Mishnah Berurah defines “still warm” in the same manner as the Shulchan Oruch HaRav or is more lenient. However, the Eglei Tal¹³ writes that the accepted custom is to follow the Shulchan Oruch HaRav’s definition, and the Igros Moshe¹⁴ writes similarly.

Therefore, in our case of the urn, it would depend on how much the water had cooled off before being turned back on. If the water had completely cooled down, reheating it on Shabbos would render it forbidden. If, however, the water was still somewhat warm when the urn was turned back on (such that most people would still use it for tea/coffee, given no other choice), it would remain permitted.

Melacha Done by a Non-Jew

There is another issue to consider in the reheating of the water on Shabbos. In the case described above, the urn was turned back on by a non-Jew. Is the reheated water still permitted even if it had fully cooled down and was effectively cooked again on Shabbos by a non-Jew?

It is clear in the Poskim that a non-Jew may not perform melacha on behalf of a Jew on Shabbos. Furthermore, if a non-Jew performs a melacha for a Jew on Shabbos, it is forbidden to benefit from that melacha, at least until after Shabbos. Even after Shabbos, one must wait בכדי שיעשו, long enough for the melacha to have been performed after Shabbos.¹⁵

However, what if the non-Jew also had himself in mind when performing the act? For example, we observed that after the water was reheated, he took a cup of hot water for himself.

The Mishnah¹⁶ states that if a non-Jew lights a candle for himself or builds a ramp for his own use on Shabbos, it is permitted for others to benefit from it as well. The reasoning is “ner l’echad ner l’meiah,” the same candle lit for one person can illuminate for many, and no additional melacha was done on behalf of anyone else. This ruling is brought in Shulchan Oruch.¹⁷

However, there is an important limitation to this rule. If the non-Jew personally knows the Jew, the benefit is forbidden, because even when acting for himself, we suspect that he also had the Jew in mind. Furthermore, he may even increase the melacha slightly in order to benefit the Jew as well. This differs from the case of a candle, where nothing additionally needs to be done for more people to benefit. Therefore, the Poskim¹⁸ rule stringently in such a case.

Additionally, Shulchan Oruch¹⁹ rules that if the non-Jew is only present because of the Jew, such as a worker employed in a home or synagogue, it is forbidden to benefit from any melacha he performed, even if he also did it for his own benefit.

Therefore, in our case, the fact that it was turned back on by the housekeeper or custodian does not help, even if the gentile did it for himself as well.

In conclusion, if the water in the urn was still warm enough to be considered drinkable as a warm beverage, then although one certainly may not ask a non-Jew to turn it back on, if the non-Jew did so on his own, the water would remain permitted. If, however, the water had cooled below that point, it would be forbidden to benefit from that hot water, since reheating it would be considered a new act of cooking on Shabbos.

1 Shabbos 74b.
2 Mishneh Torah, Shabbos 9:1. S”O 318:14. SO”H 318:24.
3 318:1. Shaar HaTziyun 318:114.
4 Shabbos 145b.
5 Beis Yosef 318:4.
6 Including solid foods which are moist.
7 Rambam, Rashba, and Maggid Mishnah.
8 318:4.
9 318:15 and 318:4. It is not clear whether the Rema holds in such a
case that it is assur min haTorah or only a d’rabbonon.
10 318:9.
11 Obviously, all rules of chazarah must be kept.
12 318:99.
13 Oifeh #8.
14 OC 4, #74 bishul 1-2.
15 SO”H 318:1, 325:9. M”B 318:5.
16 Shabbos 122a.
17 O”C 276:1. SO”H 276:6.
18 O”C 325:11. SO”H 325:17-18.
19 O”C 276:3. SO”H 276:11. M”B 276:27.