"Two birds, one stone" joke

A small boy is sent to bed by his father. Five minutes later: "Da-ad..."
"What?"
"I'm thirsty. Can you bring me a drink of water?"
"No. You had your chance. Lights out."
Five minutes later: "Da-aaaad..."
"WHAT?"
"I'm THIRSTY... Can I have a drink of water??"
"I told you NO! If you ask again I'll have to spank you!!"
Five minutes later... "Daaaa-aaaad..."
"WHAT??!!"
"When you come in to spank me, can you bring me a drink of water?"