I wouldnt wet sand with electricity - water plus electricity is bad mojo. I dont know of any waterproof sanders and wouldnt trust them if they did exist. Wet sanding requires you dunking the sandpaper into fresh water to keep the paper fresh, or by running water over the surface you are sanding. Either way, you need more water than would be safe around electricity.

If you asking - Can I dry sand up to a certain grit and then wet sand? Then the answer is yes, that works fine. Keep in mind that wet sanding keeps the paper free from clogging and keeps the paper fresh, so in my experience it actually works quite fast and "feels" like you are removing more material than a comparable grit dry sand.

But whatever you do, dont try to wet sand with an electric sander.

Bill