I'm going to pour a pitcher of ice water on a 4 year olds head
Why would you be that mean to a child?
He is disrupting my sleep when I'm in bed.
If this is a fun joking interaction you enjoy with the child and you're doing it in the spirit of fun, then go ahead. But if you plan to maliciously pour water on the child as a punishment, don't do that. Act like an adult and talk to the child; explain that you don't wish to be woken up.
You sound like a wet blanket.
I sound pretty reasonable though. I think that if this is done maliciously, that it can be classed as abuse and I do not think that that is okay.