Fact or myth-Pouring liquids backwards:
A. The custom:
Many of the populace are accustomed to not pour liquids backwards.
Below we will discuss the details of this tradition, its sources, reasons, Halachic pushback’s, and whether its practice is to be encouraged or discouraged from being followed.
B. Does it have a source?
There is no known source for this custom in any Jewish literature. [It is not recorded even amongst the writings of the Achronim who list hundreds of hazards and customs of such nature, hence implying not only that it does not have a source, but also that it was also not very widespread.]
C. The acclaimed reason for the custom:
Just as there is no record of the custom in Jewish literature, so too there is no record of its reason. Those who keep the above custom claim that it is done in order to avoid imitating actions that are done to a corpse or mourner due to a perceived Ayin Hara. However, we do not find any such recorded custom regarding a corpse. Throughout the preparation process for burial, known as the Taharah, many details are recorded in Sefarim which are based on esoteric reasons rather than the Talmud and codifiers, although nowhere do find mentioned such a concept of pouring water backwards regarding the corpse. Likewise, we also do not find recorded anywhere that a mourner during Shiva is to have his drinks poured backwards, and hence just as this custom itself has no source, its reason also does not have a source. Although, we do find among some Chevra Kadishas that they are accustomed to poor the last pouring of the Taharah onto the corpse backwards, however, aside for the fact that this itself has no source, many communities are not accustomed to do this either. Accordingly, it remains unclear as to the basis of the above custom, and as to how it started or why.
D. May a person adhere to this custom-The Halachic debate:
Some Poskim would negate the above practice, claiming that doing so transgresses Darkei Emori being that it has no logical reason or source behind it, and therefore one is to avoid doing so. Likewise, it may transgress Lo Sinacheish which is a general prohibition against believing in superstitions. However, other Poskim would rule that its practice does not involve Darkei Emori. Furthermore, some Poskim rule that it is permitted and even praiseworthy for one to believe in superstitions that the general populace believes in even if it has no source in Sefarim and the words of our sages, as the prohibition of Lo Sinacheish only applies when one verbalizes the superstition. However, even according to this opinion, it is forbidden to verbalize the superstition or Ayin Hara that if one does so he brings upon himself a bad omen for death.
Practical ruling: One who does not have such a tradition should not adapt it due to the above Halachic issues surrounding it. Nonetheless, those who received such a tradition may continue doing so if they wish in the spirit of Minhag Yisrael Torah Hi, although being careful to never verbalize the Ayin Hara.
 See Bechukosecha Eshtasheia p. 241; Maaseh Eifod 93
 It is not mentioned amongst any of the regulations recorded in relation to drinking liquids, such as that one should spill some water from the cup before drinking, which is recorded in the Poskim.
 See Rama Y.D. 177:1; Admur 301:33; Mishneh Shabbos 67a; See Rama Y.D. 178:1 “This is only forbidden if the clothing of the gentiles are worn by them for sake of frivolity [pritzus] or it is a gentile custom that has no logic behind it, as in such a case there is room to suspect that the custom derives from the Emorite customs, and that it derive from practices of idolatry passed down from their forefathers.”; Maharik 88; See Kapos Temarim Yuma 831 and Chavos Yair 234 that Darkei Emori applies towards practices that the gentiles developed as a result of idolatry, that they believed that these actions invoke their G-ds to give assistance. See also Ran on Shabbos 67a; See Admur 301:33 “Any medical treatment that works in accordance to Segulah [i.e. supernatural causes] rather than natural cause and effect [i.e. scientifically based] does not contain the prohibition of Darkei Emori so long as it is recognizable [to the onlookers] that it’s intent is for the sake of healing”; See Igros Moshe E.H. 2:13; Y.D. 4:11-4; O.C. 5:11-4; See Mishneh Halachos 12:137 “This is not a Jewish custom, and is certainly not a custom of meticulous Jews [i.e. Vasikin]…to recite ”Bless you” after a sneeze we have heard of, however what does this have to do with pulling at the ear, and one should not do so due to it being the ways of the gentiles”
 See Michaber Y.D. 179:3; Rambam Avoda Zara 11:4; Sanhedrin 65a
 See Hagahos Maimanis Avoda Zara 11:1 in name of Yireim 313; Beis Yosef Y.D. 178; Sheiris Yaakov 12; Darkei Teshuvah Y.D. 179:30; Rashba 1:167; 825; 2:281; Halef Lecha Shlomo Y.D. 115; Talumos Leiv 3:57-3
 Shiltei Hagiborim Avoda Zara 9a, brought in Pischeiy Teshuvah 179:3; Possible understanding of Rama 179:3, as initially explained in Taz 179:2; See Yerushalmi Terumos 8:3 that one needs to suspect for that which people worry of danger; Sefer Chassidim 261 that there is danger involved in matters that people believe to be dangerous; Minchas Yitzchak 9:8
 See Minchas Yitzchak ibid that this follows the famous ruling of the Rashba that the Minhag of women is holy and is to be abided. [See Rashba 1:9 and 413; Chavos Yair 134; Heishiv Moshe 13; Aryeh Dbei Ilai Y.D. 19; Darkei Teshuvah 179:23 in name of Shaar Shlomo 47; Beis Avi 2:78; Minchas Yitzchak 9:8]