Im sure its best for the rell to not get wet under any circumstances but is not too realistic when wading
If sand gets in it, it will definitely affect its performance. I usually do a gentle wipe down to remove sand and/or debris and then put a drop or 2 of oil on mine after each outing
I know for baitcasters and spinning reels it's bad for the reel to get wet. You have to break it down, clean it, and re-oil or lubricate it
Only thing is, would only be effective in water less than waist deep
BTW the lube is left over from my bait-casting days- Abu Garcia stuff in small white tubes, every reel came with a couple and a little goes a long way.