This Halacha is an excerpt from our Sefer
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Preparing before Pesach:
Some are accustomed to preparing all their drinking, and cooking water before Pesach. This is not the Chabad custom.
Why is water from the sink permitted to be drunk on Pesach? The water reservoirs from which the house water is supplied from may contain Chametz, such as kernels of grain, or pieces of bread which have been dropped there by animals, or thrown there by people. This raises the question as to whether one may drink from such water starting from the night on Pesach, as starting from the night of Pesach Chametz is not nullified even in 1000x. The Poskim throughout the ages dealt with this question and offered different Halachic reasons to justify its use. Practically, while the custom is to be lenient, as stated above, some are stringent.
The custom is to filter drinking water with a clean white cloth in order to prevent any crumbs of Chametz from being consumed. [When the Rebbe once came for the Seder in Tomchei Temimim he checked to make sure that a filter was placed by the water.]
Not to wipe lips by Mayim Achronim:
The Chabad custom is not to wipe the lips with the water of Mayim Achronim throughout all the days of Pesach.
Using hot water in a sink on Pesach:
One is initially to be careful not to use hot water that is over Yad Soledes [110° F] on Pesach, in a sink that is not Kasherable. This applies even if one has a sink insert. Thus, one should not turn on the hot water to the point of Yad Soledes and is likewise not to pour hot water into the sink so long as it is Yad Soledes, even if it is in a Keli Shelishi or Revi’i. [Accordingly, if one has a pot with hot water, he is to wait until it cools down prior to pouring it into a non-Kashered sink. One can mix cold water into the hot water in order to achieve this quicker.] If the water is warm, below Yad Soledes, it may be poured into the sink. Nonetheless, Bedieved, if one poured hot water into the sink, everything remains permitted, even it was very hot and was poured from a Keli Rishon.
 See Nitei Gavriel 2 40:5; See Otzer Minhagei Chabad Nissan p. 43 that there was a certain Chassid who was accustomed every year before Pesach to prepare all the water that he will be using for Pesach. When he came to the Rebbe Rashab to ask if he can retract this custom being that it had become too burdensome for him, the Rebbe Rashab told him that initially there would not have been an issue for him not to follow this custom, however since he already started it, he should not stop being that this was the custom of the Baal Shem Tov. The Rebbeim were not stringent to prepare water before Pesach.
 The reason: This is due to the Halachic worry explained next.
 In additional issue that some Rabbanim have raised is that in today’s plumbing system, all the waters of all the homes are connected to each other. Accordingly, if a gentile, or non-religious Jew, opens the hot water tap over Chametz, he can prohibit all the water of that reservoir. However, in truth, that most this is just a Chumra, as we do not say Nitzuk Chibur to forbid the source of the water. [See Rama Y.D. 105:3; Admur 451:59; Elya Raba 451:40; Darkei Teshuvah 105:96-100; Otzros Yerushalayim 11 p. 172]
 See Shaarei Teshuvah 467:12 that the Chametz of a gentile or Hefker does not prohibit Bemashehu; Aruch Hashulchan 467:33 that running water does not get prohibited; Nemukei Orach Chaim 467; Shevet Halevi 7:54; Tzitz Eliezer 17:23; Piskeiy Teshuvos 447:1 and 467:14
 Admur 455:9
 Otzer Minhagei Chabad p. 59
 Sefer Haminhagim p. 44
 The reason: As the sink has absorbed Chametz, as stated above, and on Pesach we are initially stringent even regarding a Keli Sheiyni transfer and even if not Ben Yomo, and even if the Chametz absorption was only due to minority usage. [Admur 451:27 and 33; 72]
 See Admur 451:34
 As Bedieved we follow majority usage by a non-Ben Yomo Chametz vessel [Admur 451:27 and 31 and 72] and hence since the sink’s majority use is with cold products, it is therefore Kosher Bedieved.