Q. Should one who was recommended by a chiropractor to sleep on a water pillow or water mattress, avoid doing so, because the water would acquire a ruach ra and you would be continuously in touch with it? Can you use that water for neigl vaser?

A. Talmud (Pesachim 112a) teaches that food and beverages left underneath a bed, even if covered in iron a ruach ra or bad spirit will rest on them. Shulchan Aruch (Y.D. 116: 5) rules accordingly that they should not be placed there. After the fact, Poskim disagree whether one can consume them them or not.
Horav Shlomo Miller’s Shlit’a opinion is that this applies to water used for drinking and not one dedicated for support and comfort purposes. Even if a ruach ra would rest on them, there is no issue with laying on them or next to them.
Shevet Halevi (8: 22: 2) debates whether such water could be used for netilas yodaim after sleeping on them, to remove the ruach ra from the hands. He permits when no other water is available.
Horav Shlomo Miller’s Shlit’a opinion is that the water should not be used for netilas yodaim since it was used for doing work (Na’ase bohem melacha), besides it is likely not fit for drinking.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a