The purest
water I can get my hands on with just
enough sea salt that the solution tastes faintly salty. Boil hard for a few minutes and let it cool. I make it about a pint at a time and keep in the refrigerator. I just put a little on a clean cloth or drop it in, doesn't matter. If my eyes are itching and red, it cures it completely and immediately, and lasts three or four hours.
I would never put anything other than cool, sterile saline in my eyes and I would never buy it in little plastic bottles from some factory.