When you are finished with your waterbomb, you should have something that looks like this.

Once inflated, the water bomb is ready to be filled.

Spread out the four corners and blow quickly into the hole.

Completed water bomb, ready to be inflated.

Valley fold the edges down and create two more locks.

Two locks complete. Turn over and repeat.

Valley fold the opposite side, and create the same lock over there.

Slide the loose flap into the pocket. This is the "lock" of the waterbomb.

Valley fold the loose edge so that it fits inside the pocket.

Valley fold the triangle vertically, creating a little pocket.