The quest of a dry bed

Day 1.

It is a disaster!

5pm Last drink of water.
8pm Peed in his lined nappy pants. LOTS
10pm Peed. (In the toilet since he refused to sleep in his bed. He knew tonight was different and couldn't sleep)
1am Peed in his Nappy pants again in bed. Kim tired and exhausted, put on pull up diapers.
8am Elliot woke up, and his diaper is wet.

Where does all the liquid come from????