I still say this is all in pursuit of unrealistic goals. Any knife you actually use will suffer a bit, chemically and mechanically. Provided with even a little bit of care, steel tools will last decades. It's not exactly like archiving cigars.

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That said, water with salts in it will cause rust faster than clean water. Our well water is so brutal that it can even corrode some types of stainless surprisingly quick. Sea water has a variety of salts in it, and is notoriously bad for metals. But any water will cause rust if you leave the steel damp indefinitely.