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One of the requirements for baking matzah is that the water used to bake the matzot must be “mayim shelanu,” water that has “rested” overnight.1 This is because water that is warm, even slightly, can cause the dough to become chametz quicker than cold water.

Water that will be used to bake matzot is drawn from a spring or well slightly before sunset and left to cool overnight.2 Some also filter the water. One should be sure that the container that the water is stored in is covered.3 The water may then be used anytime, even many days later,4 though some authorities rule that one should only use water for baking matzah that was drawn the previous night.5 It is best not to store the drawn water in metal utensils, as metal is a conductor of heat and may cause the water to become warm. So too, the utensils used to store the water should be those that have never been used to store other liquids.6 The requirement to use mayim shelanu extends to all matzot, even those that are not shmura and not used at the Seder.


There are several reasons for the requirement to use mayim shelanu. According to some, the reason is that the wells and springs are warm in the springtime, and cold water must be used for baking the matzot. Drawing the water the night before it is used allows the water to cool to the desired temperature.7 Others say that at night, in general, the water in the wells and springs are warm and thus need until the next day to cool.8

There is also a view that the water used for matzot may be drawn at any time and merely left for 12 hours before use.9 Common custom, however, is not in accordance with this view. The water used for matzot is always drawn at about sunset, with some sources recommending drawing the water bein hashmashot, between sunset and dark.10 Even in hot climates, where the wells and springs produce water that is cooler than water left at room temperature overnight, one must allow the water to “rest” overnight. This is because the decree that the water used for matzot must be left overnight applies at all times and places.11

It seems that most authorities allow one to use tap water for baking matzot (as long as it is drawn the night before use).12 Other authorities frown upon doing so, arguing that tap water frequently has fluoride and other chemicals added to it that might cause the dough to rise faster.13 So too, there is a concern that water from a city water supply may come from an open reservoir in which the water is heated by the sun.14 Nevertheless, tap water is regularly used for matzot, especially machine-made matzot, and the common custom is to allow it.

One who does not have mayim shelanu may not bake matzot.15 The only exception to this rule is for one who has no matzot at all for the holiday. Such a person is permitted to bake the bare minimum amount of shmura matzah that is needed for the mitzvah of matzah at the Seder. In such a situation, one may use any cold water to bake one’s matzot.16 So too, one who is running low on mayim shelanu may add cold tap water to the supply of mayim shelanu, as long as the original mayim shelanu is at least half, but preferably two-thirds, of the total water content.17 In addition, the water used for baking matzot should only be drawn by a Jew.18



  1. Pesachim 42a. In addition to the water having to be left overnight, a minimum of 12 hours must pass from the time it is drawn until it is used. Therefore, if sunset is at 8 pm and sunrise is at 6 am, the water may not be used until 8 am. Kitzur Shulchan Aruch 109:1.
  2. OC 455:1,3; Mishna Berura 455:4.
  3. Kitzur Shulchan Aruch 109:2.
  4. OC 455:1.
  5. Be’er Heitev 455:7; Kitzur Shulchan Aruch 109:3.
  6. Magen Avraham 455:9; Kitzur Shulchan Aruch 109:6.
  7. Rashi, Pesachim 42a.
  8. Yereim 52.
  9. Tur, OC 455:1.
  10. Kitzur Shulchan Aruch 109:1; Mishna Berura 455:4; Kaf Hachaim, OC 455:11.
  11. Mikraei Kodesh, Pesach 2:7.
  12. Halichot Shlomo, Pesach 7:3.
  13. Moadim V’zmanim 3:261.
  14. OC 455:3, 459:6; Shearim Metzuyanim B’halacha 109:3. See also Shraga Hameir 3:22.
  15. Rambam, Hilchot Chametz U’matza 5:1,2.
  16. Mishna Berura 455:36.
  17. OC 455:4; Kitzur Shulchan Aruch 109:7; Chayei Adam 128:11; Mishna Berura 455:38.
  18. Rema, OC 455:1; Kitzur Shulchan Aruch 109:5, but see Kitzur Shulchan Aruch 109:8 for an exception to this rule.

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Rabbi Ari Enkin, a resident of Ramat Beit Shemesh, is a researcher and writer of contemporary halachic issues. He teaches halacha, including semicha, one-on-one to people all over the world, online. He is also the author of the “Dalet Amot of Halacha” series (9 volumes), the rabbinic director of United with Israel, and a rebbe at a number of yeshivot and seminaries. Questions and feedback are welcomed: [email protected].