I've seen a "modern" keyboard which had been under a leaking tube for a bit too long. It still almost worked after pouring a pintful of water out and letting dry for some months. Some letters didn't work, so I opened it up to do some studying. The mechanics is like three overhead films stapled together. The outer ones have silvery lines all over on the inner side and the middle one has holes according to the keyboard layout. The idea is to press the conducting lines together through the holes to close circuits. Now in that very keyboard the water had been inside just a little bit too long, so the conductive paint (?) had washed out in one corner.
If you want to be extra careful, open the keyboard (hopefully it's made with screws instead of plastic claws), remove the electronics, rinse the three layered film and separate the layers e.g. with a rolled newspaper. The plastic parts are durable, you can wash them any way you want to. Remember, sugar doesn't mix with alcohol, so don't try any spirituous wipes or the likes.
