Shaving sharp, Not to start a huge debate, because I don't doubt that what you are saying is true. However wood ash is slightly alkaline and can be caustic. So I wouldn't leave a lot stuck to the blade if I could help it. Not sure if it would even matter, but its a thought that crossed my mind.
Fresh water is nothing to worry about, I don't get that excited about drying my knives off, better to keep them secured than laying around to dry. The ESEE plastic sheaths breath and drain well enough I think. I use mine around salt water, and so I'm pretty careful to rinse them well everyday, as the salt will put rust on almost anything given enough time, but its the same rinse that the rods and reels get every night, so its not like I treat the knives special somehow. You might get some staining, or some spotting, but you should be safe from deep corrosion over that time, especially if the knives get used. I pretty well never oil the blades either.