Q. Is it permissible to use regular bottled, filtered water for "mayim shelonu" to be mixed with the flour to make the matzah?
A. Shulchan Aruch (O.H 455: 1) based on Talmud (Pesachim 42a) rules that the water used in matza baking must be left to stand overnight (to ensure that it is allowed to cool). This water is then referred to as mayim shelanu (water which has “slept overnight”).
Although. there are different traditions regarding the who and how of the collecting of the water to be used, in principle as long as it was contained in a cool environment overnight, one may use them.
There are also Poskim that maintain restrictions as to the container the water was kept, such as metal utensils like steel or copper (Mishna Berura 455: 25, Kaf Hachaim ibid 55), and prefer the use of new and clean earthenware containers. However, they usually permit clean and new plastic containers kept protected from the sun. (Matzas Mitzva 6: 51. Piskei Teshuvos 455: n.14).
Horav Shlomo Miller's Shlit'a opinion is similar
Rabbi A. Bartfeld as advised by Horav Shlomo Miller and Horav Aharon Miller Shlit'a
Important Numbers
