If the water in the cholent pot evaporates and one is concerned that the cholent will burn, one may not add cold water to the pot, because the water will become cooked. But if there is an urn on the plata, one may pour hot water from it into the pot. If the urn has a spigot designed to let the water out, one may remove the cholent pot from the plata and pour the hot water into it by means of this spigot. If the pot is designated for meat and the urn is designated for pareve, one should first uncover the pot for approximately ten seconds, so that the pot’s steam will dissipate. One may then move the pot under the spigot, since only minimal steam will be released. If it is difficult to pour directly from the urn into the pot, one may pour the hot water into a cup and then pour it from there into the pot. This is because as long as the water is yad soledet bo, according to the vast majority of poskim the prohibition of Bishul does not apply. This is the practice of the Ashkenazic, Yemenite, and North African communities (MB 253:84; Yalkut Shemesh §88; SSK 1:17).
Others maintain that one may not add hot water to a pot on the plata, because the primary issue is not how hot the water is, but the status of the water. While the water is still in the urn, it is considered a kli rishon. When one pours out the water, its status changes from a kli rishon (which has the ability to cook food) to irui from a kli rishon (which does not have the ability to cook). Then when the water reaches the pot, it is recooked, and can once again be considered a kli rishon. There are some Sephardim who follow this opinion (Yeĥaveh Da’at 4:22). If Sephardim wish to be lenient in accordance with the opinion of most poskim, they have an opinion to rely upon (Or Le-Tziyon 2:17:8; see Menuĥat Ahava 1:3:15).
. Poskim disagree about how to understand SA 253:4. According to MA 253:16, Eliya Rabba, Pri Megadim, and Eglei Tal, SA is lenient, maintaining that as long as the water is still yad soledet bo one may add it to the pot. In contrast, some maintain that SA is stringent, following the position of some Rishonim (the second explanation brought by Rabbeinu Yona and Rabbeinu Yeruĥam) that since poured water is no longer considered a kli rishon, and can cook only the outer layer of food, one may not turn the water back into a kli rishon. Thus states Lev Ĥayim 1:99, and Yeĥaveh Da’at 4:22 and Aseh Lekha Rav 6:28 conclude likewise. A practical suggestion for those who follow this position is to fill a bag with water, seal it well, and place it in the pot. If they see that the food is drying out, they can poke a hole in the bag and the hot water will spill into the pot.This entire stringency is only relevant for those who maintain that ein bishul aĥar bishul does not apply to liquids (see sections 5-6 above). But for those who maintain that ein bishul aĥar bishul applies to liquids as well, there is certainly no prohibition. This is the custom of Yemenite Jews. Ashkenazic custom maintains that as long as water is still warm, one may heat it to yad soledet bo. SSK 1:17 is lenient, and this is also the North African custom, as explained in Yalkut Shemesh §88.
At first glance, it would seem that if the pot is used for meat, there is a problem with placing it under the urn’s spigot to pour hot water into it, because steam will rise from the meat pot and the urn will absorb the meat flavor. Later, if the urn’s water is used to make coffee, this will constitute a transgression of the prohibition of mixing meat and milk. But the fact is that this meat-flavored steam is nullified by the much greater quantity of water in the urn (assuming that there is at least sixty times more water than the steam). In addition, this is a case where the reabsorbed flavor is twice removed from the original food and has not yet become part of a prohibited mixture (noten ta’am bar noten ta’am, or nat bar nat, de-heteira), and we are lenient in such cases. Furthermore, according to Baĥ and R. Akiva Eger, if the steam can dissipate into the air, the urn does not necessarily absorb the flavor even if it is directly above the pot. Nevertheless, in order to minimize contact between the steam and the urn, one should remove the pot’s cover for about ten seconds before moving it under the urn. One should also take care not to bring the pot too close to the urn. However, even if one did not take these precautions, the urn does not become a meat vessel as a result (see Harĥavot).