Reddit mentions of Replacement for HP Pavilion HDX18 Keyboard

Water can do odd things to a laptop. With any luck, it's causing some key to read as pressed on your keyboard, even though it isn't, likely space or enter... Adding another keyboard doesn't fix this, because the two keyboards work together. Adding one doesn't make the inbuilt one shut off.
Fix: Get a replacement keyboard (there are plenty of other places that sell both used and new laptop keyboards. Just make sure the model matches)
Replacing it should be similar to the DV7 from the looks of it: http://youtu.be/XaaGma7gQqM

If it still doesn't fix it, it's possible that water got in deeper than the keyboard and is causing more problems, but this would be a good place to start.