Question: If one has a hot-water urn designated for Shabbat use and on the side of this urn there is a “water gauge” which is a thin glass tube which fills up with water in order to indicate how much water remains in the urn; every time the spigot of the urn is opened, new water flows into this glass tube through the opening that connects the glass tube to the urn until the water inside the pipe is level with the water in the urn. May one use such a hot-water urn on Shabbat or not?
Answer: The root of this question is that since the water in the tube which is there for a while gradually cools off, by opening the urn’s spigot, the cold water that until now was in the tube now re-enters the urn and gets boiled once again. The question is whether or not this is prohibited on Shabbat due to the “cooking” of the water that until now was in the glass tube and now re-enters the hot-water urn.
“Cooking after Cooking” Regarding a Liquid
We have already explained that “there is no cooking after cooking on Shabbat,” meaning that once something was fully-cooked before Shabbat, there is no prohibition to re-cook it on Shabbat. (For this reason, we permitted placing bread on a hotplate on Shabbat in order to make toast.) If so, it would seem that there is nothing wrong with the water that was previously boiled and then exited to the glass tube and cooled off re-entering the urn and re-boiling, for “there is no cooking after cooking.” However, this is not enough of a reason to be lenient in this matter since the Rishonim disagree whether or not the rule of “there is no cooking after cooking” is applied to an item that is composed of liquid. Indeed, according to Maran Ha’Shulchan Aruch, there is “cooking after cooking” regarding a liquid item on Shabbat. Thus, this alone is not reason enough to rule leniently on this matter, although there are those who disagree and permit re-cooking a previously fully-cooked liquid item on Shabbat.
A Forbidden Work about which “One does not Care”
Nevertheless, Maran zt”l writes (in his Yechave Da’at, Volume 6, Chapter 21) that an additional reasoning may be added to rule leniently in this case, for when one uses such a hot-water urn on Shabbat, he does not care at all about the fact that the water in the tube is re-entering the urn and becoming re-boiled there. Thus, this is considered a “directly-resulting forbidden work about which one does not care,” meaning that although the re-boiling of the water will certainly occur, nevertheless, the person does not care about the forbidden work that results. Several Rishonim, including Rabbeinu Natan, author of the Aruch, the Rif, and others, are of the opinion that any such “directly-resulting forbidden work about which one does not care” may be performed on Shabbat. Although we rule that a “directly-resulting forbidden work about which one does not care” may not be performed on Shabbat, nevertheless, regarding the usage of such a hot-water urn we have a double-doubt that allows us to be lenient: Firstly, perhaps the rule of “there is no cooking after cooking” applies even to liquid items, and secondly, perhaps the Halacha follows the author of the Aruch who says that there is no prohibition to perform a forbidden work on Shabbat about which one does not care.
Thus, halachically speaking, one may use such a hot-water urn on Shabbat without any issue. Hagaon Harav Yosef Shalom Elyashiv zt”l and others ruled likewise.
