Question: [Monday 11th Elul, 5780]
What is the halacha for opening bottles on shabbos? Im talking about soda bottles, grape juice bottles – they have usually a white plastic cap, that once opened leave a plastic ring on the neck of the bottle.
You may be lenient to open them on Shabbos. However, I suggest initially opening it before Shabbos, or having a child open it on Shabbos. Again, if not possible, you may open it on Shabbos
Background: Opening a metal or plastic bottle caps on Shabbos is under the question of whether it transgresses the Rabbinical prohibition of Tikkun Keli [as its done with ones hands, without an instrument and is thus at best only Rabbinical] and/or Michateich, and is practically debated amongst Poskim of today with some siding that it is allowed even by metal caps, and some allowing it only by plastic caps [due top Tikkun Keli] and some forbidding it even by plastic caps [due to Michateich]. The reason behind the leniency by plastic caps versus metal caps is because they were already fully usable prior to being attached to their ring and often remain usable even when attached to the ring and hence the removing of the ring is Halachically meaningless, and is similar to one who got his plastic fork stuck in an item and he pulled it out of that item in order to use. Practically, the widely accepted approach is to be lenient by plastic caps, although nevertheless I do as I suggested above and try to avoid any even questionable Shabbos prohibition when possible.
Sources: Rav SZ”A permitted by plastic caps and not by metal caps; Rav Elyashiv forbade even by plastic caps. See RSZ”A in Minchas Shlomo 91:12; Divrei Moshe [Rav Moshe Halbershtam] 12-13; Minchas Yitzchak [see Divrei Moshe there]; Rav Moshe Feinstein [brought in Revivos Efrayim 4:96]; Az Nidbaru 3:40; RSZ”A in SSH”K 9 footnote 61; Yeshuos Moshe 3:27; Chazon Ish 51:11; Kinyan Torah 5:34; Beir Moshe 3:90; Even Yisrael; Cheishev Haeifod 3:93; Mishneh Halachos 7:47; Dvar Yehoshua 2:45; Tzitz Eliezer 14:45; Lehoros Nasan 7:21; Halichos Sadeh 14 pp. 107-137 in great length
Question: [Sunday 10th Elul, 5780]
May one use an in sink water filter on Shabbos?
Practically, if there is no actual seeable sediments/dirt/etc in the water that is being filtered out, then you may use the filter on Shabbos. The Issur is only if there is a substance apparent to the naked eye which is being filtered out, and you, or most people, would never drink the water without it being filtered. Nonetheless, some are stringent not to use a filter on Shabbos, although the widespread custom is to be lenient as stated above.
Sources: Admur 319:13; Rama 319:10; Shabbos Kehalacha Vol. 2 P. 346-347; Shabbos Kehalacha p. 361 based on ruling of Rav SZ”A 3 footnote 163 regarding Pesach cloth of which the allowance to use it is due to that one is not certain that it contains Chameitz, and Minchas Yitzchak 7:23, Ketzos Hashulchan 125 footnote 37 and others that by waste which is only questionable if contained within the liquid, the separating prohibition does not apply. So is also implied from the Lashon of the Peri Megadim which is the source for the stringency which mentions “water that has small twigs” in his case of a particular type of person; Poskim brought in Orchos Shabbos, mentioned in Shabbos Kehalacha ibid footnote 52; See here for the full details of this subject: https://shulchanaruchharav.com/halacha/filtering-liquids-with-a-filterstrainer/