the membrane contact will never dry. It's 3 pieces of plastic placed just far enough apart to trap any spilled water. your continuous use has probably caused the conductive ink used to create the contacts to burn off due oxidation or shorting.
what can you do?
open the keyboard up, separate the membranes and allow them to dry. use some gloves while you are doing this. your finger oils are not good for the conductive ink. wipe with rubbing alcohol swabs if needed. if you see black crap, you need to go to radioshack and buy a conductive ink pen to repaire the damage to the conductive ink traces, if needed.