Yes, some (most of the modern keyboards) are made of a folded mylar sheet with a printed circuit pattern on it and holes in the middle layer so the upper and bottom layers can be brought in contact and back out again at positions corresponding to the keys.
Water will get between the layers and it will not come out unless one disassembles the keyboard.
Washing membrane based keyboards has a poor prognosis but if it's dead anyway, why not give it a try. Just be sure to disassemble it and unfold the membranes. And dry them thoroughly before reassembly.
Keyswitch keyboards are generally washable.