Filtering Cloudy Water on Shabbos

Q. Is there a permissible way to filter cloudy water on Shabbos?

A. Mishnah Berurah (319:40) writes that if a liquid other than water is partially cloudy and is still potable, some poskim permit filtering the liquid on Shabbos if two conditions are met: the liquid must be filtered through a cloth which is considered a shinui (an unusual manner for filtration), and the liquid must be needed for “immediate use,” i.e., for the upcoming meal. Nonetheless, the Mishnah Berurah (319:42) writes that not all agree to this leniency, and it is best to be strict unless there is a pressing need.

Cloudy water cannot be filtered in this manner because pouring water on a cloth on Shabbos violates the melacha of libun (washing). Pouring other liquids on a cloth does not constitute libun, because the liquid will stain the cloth.

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The Gerald & Karin Feldhamer OU Kosher Halacha Yomis is dedicated to the memory of Rav Yisroel Belsky, zt"l, who served as halachic consultant for OU Kosher for more than 28 years; many of the responses in Halacha Yomis are based on the rulings of Rabbi Belsky. Subscribe to the Halacha Yomis daily email here.