Summary of the requirements needed to be allowed to add hot water to ones Cholent on Shabbos:[1]

1. Both the water and the Cholent are fully cooked.[2]
2. The water is poured directly from the boiler to the Cholent, without placing the water in any pot in-between. [However, regarding using a spoon or ladle, see above Q&A15]
3. The cholent pot is on a source of heat which is covered. If one is using a crock pot or electric plate which does not have variations of heat settings, it does not need to be covered.
4. Pour the water in slowly in order so the cholent that is on the fire does not mix due to the pouring. Thus, it is best, although not obligatory, to remove the cholent from the fire [fulfilling all the Chazara conditions], poor the water in it and then return the cholent to the fire.
5. In order to keep the water boiler Pareve, one must be careful to distance the boiler from the cholent to avoid it splashing onto the boiler. Likewise, the steam of the cholent should not directly hit the boiler. Thus, one should delay after uncovering the cholent for the steam to dissipate.

There is no problem involved with the fact that the stream of water from the Pareve boiler is touching meat, as this is only problematic when the item being poured is cold. However, when both are hot, as is the case here, this is allowed even initially.[3] [However there are Poskim[4] which are stringent in this matter to initially avoid pouring even from hot Pareve to hot meat.]

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[1] Shabbos Kehalacha 9:40 [p. 389]; See Piskeiy Teshuvos 253:24

Other opinions: Some Poskim hold one may never pour hot water from a Keli Rishon into a Keli Rishon due to a cooking prohibition. [See Michaber 253:4; Yechaveh Daas 4:22; Lev Chaim 1:99; Oar Letziyon 2:17-8; Piskeiy Teshuvos ibid footnote 231]

[2] If the water is being placed to prevent the food from burning, then it is considered fully cooked if it is Yad Soledes. If however it’s being placed to add the amount of gravy to be eaten, then according to some, it must have had previously boiled. However the main opinion is like the former.

[3] So rules Rav Farkash ibid.

[4] See Darkei Teshuva 105:96; Yad Yehuda Hakatzar 105:31; Peri Megadim 105 M.Z. 6. [See “A Semicha Aid for The Laws of Taaruvos” Chapter 105 Halacha 4 for a full analysis on this subject!] Appendix!

Opinion of Admur: In 451:59 Admur rules that women are accustomed not to use on Pesach the urn they pour from in order to Kasher an item, being that the steam of the Chameitz vessel which is being Kashered becomes absorbed in the vessel. This implies that Admur is stringent even when pouring hot onto hot. [See Piskeiy Admur p. 330] Vetzaruch Iyun if anything can be deduced from this law as Admur writes only “there is an opinion which explains”, as well as it is merely a custom, as well as the upper vessel certainly should be permitted, as Bedieved we do not hold taste is transferred. Thus one must conclude that it is a Pesach stringency that is not relevant to other Issurim, and so writes Shabbos Kehalacha ibid, as is also evident from Darkei Teshuvah 105:99