Is it permissible to drink water that was left uncovered overnight?

Greetings,

According to the law, there is no prohibition against leaving water uncovered both during the day and at night, and it is permissible to drink it afterward, since snakes are not commonly found among us. Nevertheless, one who is cautious should ideally avoid leaving water uncovered both during the day and at night. 

Sources: The Shulchan Aruch, Yoreh De'ah (section 116, paragraph 1) states that sages prohibited uncovered liquids due to concerns that a snake may have drunk from them and left venom in them. However, now that snakes are not commonly found among us, it is permitted. But see Pithchei Teshuvah there (note 1) in the name of the Shelah, that nevertheless, one who guards his soul should distance himself from this. Moreover, the pious Rabbi Eliezer Waldenberg zt”l was very careful about this matter. Additionally, the Chida zt”l in She'eilot u'Teshuvot (note 3) wrote that the custom in the land of Israel is to be cautious about this. Further, see in She’eilot u’Teshuvot Shevet HaLevi part 6 (section 63, note 2) and in She’eilot u’Teshuvot Olat Yitzchak part 2 (section 178) that nowadays there is no concern whatsoever according to the law. For a comprehensive discussion on this topic, see the book Shmirat HaGuf VeHaNefesh part 1 (section 44).

In the book Beit Yehudi part 10 (page 70), it is written in the name of Rabbi Ovadia Yosef zt”l that in any case, if one has left drinks uncovered, they should not be prohibited retroactively and it is permissible to drink them. Further, see in the book Asheri Ha'ish part Orach Chaim part 1 (chapter 1, paragraph 15) and in She’eilot u’Teshuvot Yisa Yosef part 2 (section 15).

Blessings,

Hillel Meirs