For many kids they sleep WAY too soundly. We bought an alarm for our oldest son's underwear (he was in first grade). When the alarm detected wetness it sounded off. We thought it would wake the baby in the room next door, but the baby slept right through it.
Amazingly our oldest slept through it too! In the beginning we still had to wake him up and walk him to the bathroom. Then he would wake up on his own, but be so confused he would just twirl around his room. Then he made it to the bathroom but left the lid down, peed on the closed lid and went right back to bed. Finally, after MONTHS of patience it worked!! Ultimately they realize the urge and wake up on their own, without the alarm.
This situation is so painful for an older child. Please don't wait any longer. Get the alarm. Waking them up in the middle of the night doesn't work, because their brain doesn't learn the sensation of "I have to use the bathroom." Instead it learns, "My mom is waking me up." Nor does giving less water...
We also went to a pediatric specialist to make sure nothing else was wrong.