Expanding slightly on the above answer;
Question: Why, after a plane has crashed into the water, do investigators put the "black box" back in water? – Will Cowger, Houston Answer: If a flight data recorder is recovered from the water, it is submerged in fresh, clean water to prevent deposits such as salt or minerals from drying out within the device.
When the technicians at the laboratory are ready to download the data, they take the recorder out of the freshwater bath, carefully open it and dry any sections that have been exposed to water. They then download the data into special computers that can read the information.