Waters Fit for Netilat Yadayim
- One needs a reviyit of water in one place for netilat yadayim. Really one reviyit suffices for both hands, but for many reasons it is appropriate to have a reviyit for each one.
Water Left Uncovered, under a Bed, or in a Bathroom
- Water that was left uncovered is fit for netilat yadayim as long as there isn't a concern of a snake drinking from it in that location.
- Water that entered a bathroom shouldn't be used for netilat yadayim but in extenuating circumstances if there's no other water available it can be used.
- Water that was left underneath a bed shouldn't be used for netilat yadayim but if in extenuating circumstances if there's no other water available it can be used.
- Colored water is unfit for Netilat Yadayim. The same law applies whether the color changed because something fell into it or because of the container. 
- If a dog would not drink the water then it is unfit for Netilat Yadayim. 
- If dye changed the color of water even if it didn’t dissolve the water is unfit. 
- If dirt fell into water it is not considered water that changed colors. 
- If water that changed its color changed back to its normal state it is considered fit for netilat yadayim. 
- If one does Tevilat Yadayim in a mikvah, the waters are fit even if the waters changed colors unless dye, red wine, or fruit juice fell in and dissolved. 
- Water which comes out of the faucet white and turns clear after some time is fit for netilat yadayim.
- Scented water is fit for netilat yadayim if the scent was added to improve the water.
- Water that was used for netilat yadayim once is unfit for netilat yadayim again. But if someone didn't wash netilat yadayim yet and he touched the water he doesn't render it unfit for netilat yadayim.
- Water that was used for some purpose may not be used for netilat yadayim. Examples of purposes for which water would be rendered unfit include using water to wash dirty dishes, launder clothing, clean vegetables, and measure something.
- Water that an animal drank from is fit for netilat yadayim. Water that a dog or pig drank from shouldn't be used for netilat yadayim.
- Water of a mikveh or spring can't be rendered unfit because of work as long as it is attached to the mikveh or spring.
- Hot water is fit for netilat yadayim. Some say that if the water is Yad Soledet Bo it is unfit.
- Water that is bitter or dirtied with mud is fit if a dog wouldn't drink it but is fit if a dog would drink it.
- Snow or ice is fit for netilat yadayim only after it melts into water.
- Snow that isn't melted and connected to other snow so that together it constitutes forty seah is fit for dipping one's hands in for tevilat yadayim only in extenuating circumstances when water is unavailable.
- Ice from the freezer that was melted is preferable not to use since nowadays it is common to spill out that water.
- Shulchan Aruch OC 160:14
- Mishna Brurah 160:67
- Halacha Brurah 160:6
- Halacha Brurah 160:7
- Halacha Brurah 160:8
- Shulchan Aruch 160:1 writes that the law of waters that changed it’s color is the same whether the color changed on it’s own, because of something falling in, or because of the container. Mishna Brurah 160:2 writes that the Achronim point out that the S”A merely copied the language of the Tur, however, we hold like the Rambam and so it’s permitted.
- Kitzur Shulchan Aruch 40:10
- Mishna Brurah 160:2
- Mishna Brurah 160:3
- Mishna Brurah 160:5
- Mishna Brurah 160:4
- Or Letzion 2:11:7 explains that water which comes out of the faucet white is fit for netilat yadayim since it isn't really colored with a pigment or dirt, it just appears white because of the air bubbles. Also, the Pri Megadim says that a coloring which is only temporary doesn't render the water unfit for netilat yadayim. Halacha Brurah 160:4 agrees.
- Mishna Brurah 160:12, Halacha Brurah 160:17
- Rama 160:11
- Shulchan Aruch 160:2 writes that water that was used for melacha is unfit for netilat yadayim and the Mishna Brurah 160:6 explains that once the water was used it is ready to be discarded.
- Shulchan Aruch 160:2, Mishna Brurah 160:8 and 11
- Shulchan Aruch OC 160:4
- Mishna Brurah 160:23, Halacha Brurah 160:20
- Shulchan Aruch OC 160:5
- Shulchan Aruch OC 160:6
- Mishna Brurah 160:27
- Shulchan Aruch OC 160:9
- Shulchan Aruch OC 160:12. The Magen Avraham 160:16 ponders why snow wouldn't be allowed to be used for netilat yadayim if it is acceptable for tevilah in a mikveh (Shulchan Aruch YD 201:30). He concludes that tevilat yadayim would work in snow even if it isn't melted but for netilat yadayim it needs to be melted.
- Mishna Brurah 160:58
- Halacha Brurah 160:16