http://kidshealth.org/kid/health_problems/bladder/enuresis.html#
If you wet the bed, there are some things you can do to stay dry. Try not to drink anything after dinner and remember to go to the bathroom before going to bed. If you do wet the bed, help with the cleanup by pulling off the sheets and putting them in the laundry.
A lot of doctors think that the best treatment for enuresis is a program that retrains your brain to do one of two things:
1. wake you up so you can go to the bathroom
2. stay asleep and hold it until morning
This program includes doing bladder exercises, such as waiting a little longer to pee during the day, reading about and imagining staying dry, or even using a tiny alarm. The alarm is connected to a pad placed in your underwear at night. If you start to urinate, the pad senses the moisture and sets off the alarm. Different alarms buzz, vibrate, or do both, but they're all easy to use and can help wake even the deepest sleeper.
There are medicines for kids who wet the bed. They might help you temporarily, but they don't cure bedwetting. These medicines work best when combined with the alarm or other training programs.
It may take some practice to retrain your brain, and you'll need to be patient. But eventually, you will stop wetting the bed.