A custom of many Jews, including Chabad, is to be careful not to let the Matzah get wet. According to this custom, we don’t have Matzah balls or Matzah Brei. This is because of a concern that there may still be some flour in the Matzah which, if combined with water, would become Chametz (leaven). The Rebbe King Moshiach Shlita, in his majesty’s commentary on the Hagaddah, says to keep the Matzos covered so water won’t spill on them (and at the designated times in the Seder for uncovering the Matzah, we uncover it a little bit), and also that before pouring liquid we should check that the bowl or cup does not have Matzah crumbs in it.
On the eighth day of Passover, however, we do mix Matzah and water, and even go out of our way to do so. Then we can enjoy Matzah balls and Matzah Brei!
