Hi Oscar! Thought I would throw my 2 cents in in case you are asking for potty training reasons...
Just pt'd DS1 2 weeks ago. (and it way sooo much easier and faster than I thougt!) We didn't do nap/bed training, just daytime. He wakes up soaked too, and we just started using a diaper one size up to help handle any leaks. I don't feel like we were necessarily giving him a ton to drink at night, like others said here.
BUT, now that he is pt'd by day, he has started to not pee in his diaper at night, but instead wakes at 5am!!!! to tell me he has to go pee pee. Then, we NEVER go back to sleep after that. I suspect that is the time that he normally peed in his diaper and now that he knows the sensation, he wakes up. Sometimes he still goes in the diaper, but the 5am wakings sitll happen. If anyone can help me wtih THAT crazy thing, let me know.
Good luck!