It occasionally happens on Shabbat morning that a person notices that his Hamin (cholent) has begun to dry, such that it would likely burn by the time he returns from the synagogue later in the morning. In such a case, is it permissible to add water from an urn or kettle to prevent the Hamin from burning?
It is clear according to all authorities that Halacha forbids pouring hot water into Cholent as it sits over a fire (even a fire covered with a "Blech"), on a hotplate, or in a crockpot. So long as the food is over fire or on an electric heating element, one may not add water to the pot. The question under discussion relates to whether one may remove the pot from the fire or heating element and then add water. At first glance, this should be permissible. Since one pours hot water directly from an urn or kettle, it does not become hotter upon entering the pot of Hamin. Seemingly, then, no prohibition of Bishul (cooking on Shabbat) is entailed.
In truth, however, the Shulhan Aruch rules (in Orah Haim 253:4) that this is forbidden. Although the hot water indeed originates from a Keli Rishon (the original utensil in which it had been boiled), its heat diminishes once it is poured out of that utensil. Halacha considers the heat of "Iruy Keli Rishon" – liquid poured from its original utensil – as slightly lower than that of liquid in the Keli Rishon. Hence, once the poured water enters the Cholent pot its heat intensifies, thus qualifying as a violation of Bishul. It is therefore forbidden to add hot water to a Cholent pot on Shabbat even directly from an urn or kettle, and even if the pot had been taken off the fire or heating element. The Shulhan Aruch adds that those who act leniently in this regard must be admonished and instructed not to do so. (It goes without saying that one may not collect hot water from an urn or kettle in a different utensil and then pour it into the Cholent pot.)
This is indeed the ruling of Hacham Ovadia Yosef, as he writes both in Halichot Olam (vol. 4, p. 61) as well as in Yehaveh Da'at (4:22). Hacham Ovadia adds, however, that if a person did add hot water to his pot of Hamin on Shabbat, the Hamin does not become forbidden for consumption on Shabbat. In such a case, he explains, one may rely on the view among the authorities that "En Bishul Ahar Bishul Be'lah" – once a liquid has been cooked, repeated cooking does not constitute a violation of Bishul. Although we do not accept this view as authoritative Halacha, one may rely on this position after the fact, if a person mistakenly added hot water to Cholent.
Hacham Ben Sion Abba Shaul (Israel, 1924-1998), in his work Or Le'sion (vol. 2), likewise rules stringently on this issue. He adds, however, that since an argument could be made to allow adding the hot water in this case, those who act leniently in this regard need not be admonished. Nevertheless, as stated, Hacham Ben Sion rules that one should not add hot water to a pot of Hamin on Shabbat.
It is therefore advisable to take precautions before Shabbat to ensure that one's Cholent will not dry out before lunchtime on Shabbat. One possibility is to keep the crockpot slightly elevated within the heating element, which has the effect of slowing the cooking process. Likewise, one who cooks Cholent on a Blech can place it off to the side where there is less heat. The most advisable solution is to fill a cooking bag with water and place it inside the Cholent pot before Shabbat, where it functions as a "reserve supply" of water. If one notices the Cholent drying out, he can simply puncture the bag and allow the water to flow into the Cholent. Since the water is already cooked inside the pot, it is permissible to allow the water out of the bag to mix with the Cholent. If the Hamin does not begin to dry, then one simply removes the bag of water and pours it into the sink.
Summary: It is forbidden to add hot water to a Cholent pot on Shabbat to prevent it from burning. One should therefore take precautions before Shabbat to ensure that the Cholent will not dry out before lunchtime on Shabbat.