The balloon is widely known as the water balloon, but since it is made of paper it cannot hold water very well.
You need to first fold the Waterbomb base.
 1) Fold the Waterbomb base and position it so that it opens up on the bottom. |
 2) Fold the top wings up so it makes a diamond. |
 3) Repeat step 2 on the back. |
 4) Fold the top layer's sides to the center. Eyeball the center. |
 5) Fold the top layer's points at the top down along the edge of the paper folded down in the previous step. |
 6) Fold the little triangles made in the previous step into the middle, halving the triangle. |
 7) There should now be a little pocket underneath the top triangle. Fold the top triangle into it so it disappears. |
 8) Flip over, then repeat steps 4-7. |
To fill it with air/water:
There should be a little hole on the bottem of the model.
Put your lips to it, then blow air into it.
You may have to shape the balloon some with your fingers.
Once you fill it with air, put it under a trickle of water to fill it up.