Why do ADD/ADHD people bedwet? Some have specific causes such as diabetes mellitus, diabetes insipidus, anatomical deformity of the bladder or its outflow tract, and the like. If no obvious medical cause can be found, then it is labeled as primary nocturnal enuresis (bedwetting without an obvious cause and presumably due to inherited brain chemistry). Primary nocturnal enuresis happens because the ADD/ADHD individual is less able to wake up when the urinary bladder is full or be awake enough to get up and go to the toilet when the urge to urinate is present. Difficulty waking in the middle of the night is similar to difficulty waking in the morning which is present in 91% of those with ADD/ADHD.
It is sad that bedwetting is still a very under-appreciated clue to ADD/ADHD neurology even by health professionals. In my experience based on 1822 cases, 48% of those with ADD/ADHD are or have been bedwetters. About 40% of adults who are asked if they have a history of bedwetting are able to remember such a history while about 8% do not recall or have suppressed awareness entirely. By the way, none of my patients have ever considered bedwetting as a positive experience. Most are still embarrassed even to talk about this problem. I bedwetted nearly daily until I was about 10 yr old.
I don't think I ever actually wet my bed when I was a child. At night, I somehow always got out of my bed, but ended up peeing in the hallway (I think it stopped by age 9). It was quite embarrassing, especially when I wouldn't remember it the next morning and there would be a huge wet spot on the carpet. 
I don't know if that is more of a "can't find the toilet when you're sleepwalking" issue, but it may be related to the ADHD/bedwetting connection.