Coffee Urns left out throughout the week?

Question

Many people still keep to the halacha that one isn't allowed to drink from water kept in metal overnight.

• How would one be allowed to drink from a Coffee Urn on Shabbos?
• How could one drink from a can of soda?

Answer 1

The footnotes there in Shulchan Aruch Harav refer, among others, to a letter by the Lubavitcher Rebbe zt"l (Igros Kodesh, vol. 2, pp. 143-145), in which he discusses this issue. He concludes that this is one of those examples of things that "since many people are accustomed to doing it, then shomer pesayim Hashem, 'Hashem guards the simple.'"

[He notes that this particular rule seems to be a non-scientific type of danger (ענין סגוליי), and therefore this rationale can be used to ignore it entirely - unlike things that are indeed recognized as potential medical dangers to health, where even shomer pesayim only mitigates the danger but still requires one to take appropriate precautions.]

With soda cans, anyway, we might not even need that consideration. In the paragraph before that the Rebbe suggests that the word keli should be understood as narrowly as possible. So we can suggest that sealed soda can is not a keli, because it has no opening (as indeed is the case as far as hilchos Shabbos).