Is this the capacitive type or the membrane type? My understanding is that liquids kill the membrane-type model Ms very quickly, which is why they sprouted drainage holes when IBM switched from the capacitive buckling springs to the membrane buckling springs.
(Liquid does not permanently kill the membrane, it's just that liquid gets stuck between the two membranes and can't get out. You can disassemble everything, dry it, and get it working again. Probably. I haven't tried it.)
I have spilled on my Topre keyboards before and there is no fix but to take everything apart and dry the individual pieces. The keyboards are quite well made so can take many cycles of this careful cleaning. To me, that's the best you can hope for; water is not good for keyboards. Though you can probably use Hall effect keyboards under water, if the driving electronics are conformally coated.
The capacitive keyboard was the Model F. Instead of the plastic barrel frame, it uses separate plastic barrels held between two metal sheets, and the little conductive plastic flippers trigger capacitive pads on a PCB. https://deskthority.net/wiki/IBM_Model_F
“This source here” is wrong (as was pointed out in the comments below in 2014). It is just misquoting Wikipedia, which it links to: “In a Model M, the electrical contact is a membrane sheet similar to that of a modern dome switch keyboard. On the older Model F design, a capacitive contact was used instead.”
Go ahead and take a Model M apart. I guarantee you’ll find a membrane sheet.
(Liquid does not permanently kill the membrane, it's just that liquid gets stuck between the two membranes and can't get out. You can disassemble everything, dry it, and get it working again. Probably. I haven't tried it.)
I have spilled on my Topre keyboards before and there is no fix but to take everything apart and dry the individual pieces. The keyboards are quite well made so can take many cycles of this careful cleaning. To me, that's the best you can hope for; water is not good for keyboards. Though you can probably use Hall effect keyboards under water, if the driving electronics are conformally coated.