By: Halacha Yomis Team of OU KOSHER

May One Filter Water On Shabbat Using A Special Filtering Device?

Shulchan Aruch (OC 319:10) writes that one may pour clear wine or clear water through a filter on Shabbat to remove impurities, provided the liquid is drinkable without filtration. Since the particles do not prevent one from drinking the water, removing these particles is not treated as “borer” (separating “pesolet” from “ochel” -bad from good).

This is not the position of the Rambam, who does not allow the use of a filter on Shabbat under all circumstances, but the halacha follows the lenient view.

The Mishnah Berurah (319:34) writes that poskim dispute to what degree must the liquid be potable to allow filtration. The Bach requires that it be suitable for everyone, but most poskim maintain that filtration is permissible if most people would drink the water or beverage. The latter opinion is generally followed.

The Mishnah Berurah (Beiur Halachah s.v. ho’il) adds that a fastidious person who would not drink the liquid without filtration, may not do so on Shabbat, even though the majority of people would not care. Rav Elyashiv (cited in Hilchos Shabbat B’Shabbat 1:9, note 32) writes that a fastidious person only refers to one who would not drink the liquid even under extenuating circumstances (such as when they are very thirsty).