This Halacha is an excerpt from our Sefer
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On the night of the Seder: On the night of the Seder, one does not fulfill his obligation of eating Matzah, with Matzah that is cooked in water being that its taste has been nullified. Furthermore, Lechatchilah one may not even fulfill his obligation with Matzah that is dipped in water, as the Matzah must be eaten plain. However, Bedieved if one did so, he fulfills his obligation. Furthermore, a sick or old person may be lenient to do so even initially if they cannot eat the Matzah otherwise. One however does not fulfill his obligation with Matzah dipped in fruit juice, even Bedieved, being that it removes the taste of the Matzah.
The rest of Pesach: The Chassidic custom is not to eat any Matzah dipped in water due to a suspicion that part of the flour may not have been kneaded into the dough and thus now when it will come into contact with the water it will become Chametz. On the last day of Pesach in the Diaspora, one who is lenient to eat Matzah with water for the purpose of Yom Tov joy, is not losing out on keeping of the above-mentioned stringencies of the Arizal. Regarding dipping Matzah in fruit juice, it’s obvious that one need not be stringent against doing it throughout the entire Pesach. See Chapter 7 Halacha 3 for further details on this matter!
What does an old or sick person do if he cannot eat hard Matzah?
He may be lenient to eat Matzah dipped in water for the Seder night. One needs to dip a Kezayis in the water, and needs to make sure that the Matzah is not cooked and has not stayed 24 hours in water, otherwise he does not fulfill his obligation.
 Admur 461:14
 Admur 461:12-14