Why does Robert Redford pour water on his radio and a cellphone?

Redford pours water on the electronics to remove conductive sea salt from them so that they can dry out and can (hopefully) be used again. He tries to use the radio the next day by connecting the boat's service battery to it.

"The next day he continues patching the hole in the side of the boat and pumping more water. It's slow, exhausting work. He pulls out the radio equipment and pours bottled water on the interior of the devices to remove conductive sea salt from them. He sets them out to dry on deck. The next day, he's able to complete cleaning the cabin with a sponge and mop. His fiber glass patch seems tentative, but at least keeps water out. He drags one of the boat's service battery on deck and hooks it to his radio. The radio does not work. He consults his navigation charts. He goes below and as he's looking through a book on celestial navigation, he hears someone speaking on the radio. He hurries back up on deck and makes an SOS call. It doesn't appear to work before the radio goes dead."

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