Is one to cover the Negel Vasser water at night prior to going to sleep?
Many opinions rule there is no need to be stringent against washing hands with water that was left revealed overnight. This applies even in an area where snakes are commonly found. However, there are opinions who are stringent and rule one is to avoid washing with revealed waters. Practically, the custom is to be lenient completely even regarding drinking revealed waters, and certainly regarding using it for washing, and so is the apparent Chabad custom. There is likewise no problem to wash hands for bread using revealed waters even in areas that snakes are common.
 See Hakashrus p. 432; Piskeiy Teshuvos 4/12
 Shalmei Tzibur brought in Shaareiy Teshuvah 4/7; Pischeiy Teshuvah Yoreh Deah 116/1; Peri Toar Yoreh Deah 116/2; Birkeiy Yosef 116/4; So is also implied from M”B 160/23; Admur 272/1 rules we are no longer careful regarding revealed waters as snakes are no longer commonly found.
 Shalmei Tzibur ibid, as the stringency of not drinking from revealed waters in areas with snakes only applies to drinking and not washing. [Shaareiy Teshuvah ibid; M”B 160/23]; See however Poskim in next footnote that one is to be stringent in those areas that snakes are common.
 Rav Sheptal brought in Shaareiy Teshuva ibid; Seder Hayom: “Every G-d fearing Jew needs to prepare for himself prior to going to sleep two vessels, one that contains water and one that is empty, into which he will pour the water upon awakening. One is to place the water filled vessel into the empty vessel, covered and clean.”; Chesed Lealafim 4/10; Kaf Hachaim Falagi 8/11; Kaf Hachaim 116/8 and Artzos Hachaim 4/1 that one is to be stringent in those areas that snakes are common [brought in Hakashrus 18/19]
 Conclusion of Shaareiy Teshuvah ibid
 See Migdal Oz story 114 from which it is proven that it was not an acceptable Chabad custom to cover the waters. This is seen from the fact the apprentice of the Tzemach Tzedek could not understand why he covered the water, as well as from the fact one Chassid complained to the Rebbe Rashab about the stringencies of another Chassid who followed this ruling of covering the water. Nevertheless, as is evident from the story, this was the custom of the Tzemach Tzedek. However from his response it is understood that this custom is not meant as a directive for the public.
 Levush 160/5; Aruch Hashulchan 160/1; M”B 160/23 [It is implied from there that he rules even regarding washing hands upon awakening there is no need to be stringent]; See however Kaf Hachaim 116/8 that one is to be stringent in those areas that snakes are common.