Preserving sausage casings
+1 for salting.
Do NOT skimp on the salt. Cheaper to use a pound of kosher salt than to toss the casings.
Salted, in a sealed container, into the back fo the fridge and you're golden. I've kept casings for well over a year this way.
Get the entire length of all the casing in contact with the salt. Don't just pour a bunch of salt on the "glob" of casing. Work the salt in there. You're seeking to use the salt to desicate the casings.
Is the water salted? I haven't seen casings that weren't packed either in salt or in brine. If it's not salted, I would add salt to the water. Casings should last at least six months in the fridge, maybe even up to a year. Although I have frozen salted casings successfully for a short period of time, most sellers of natural hog casings recommend against it.