Getting cards wet can definately destroy them. They are not waterproof and two things can happen that will kill the card. They are electrical shorts and corrosion.
The most important thing is to get them dry before powering them up again. If they fell into saltwater or something really corrosive I dont think I would trust them again, I may use them in a cheap Mp3 player but not anything important.
I have seen images recovered from cards that survived hurricanes and typhoons so it is possible to save them.
I dropped one in a mud puddle and managed to get it cleaned up and am still using it today. Fortunately the card wasnt powered when I dropped it so I didnt have any short circuits here is what I did.
1: Immediately I wiped the card off and placed it in its plastic case.
2: On returning home I rinsed the card with distilled water.
3: Next I wiped the card off and placed it out on a paper towel to dry for a few days.
4: I then took a sealing plastic box like a tupperware and filled it halfway with rice. I took the card and folded paper around it and layed it on the rice. Then filled the container with rice and let it set for a few days. ( The rice will soak
up the moisture left in the card you could use silica gel as well)
5: The card fired right up and was fine.
In that case it wasnt in the water long, I think if I had one soaked in saltwater I would crack it open and rinse it with
distilled water then glue it back together after drying. Saltwater would definately start a corrosion process.
I have had cards that I spilled coffee on that were recovered in the same manner. The main thing is too get them out of the liquid as quickly as possible and then take your time drying them before powering them back up.
I havent done it but have heard of people recovering data from phones and cameras that got wet while the power was on. The main thing is to get the card and batteries out of the device as soon as possible. The procedure would be the same as above but your odds of recovering data are much lower, still worth trying however.
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