In the 15th level ("Ventilation Shaft") of "Boiling Point" in Where's My Water?, the collectible item does not appear. Restarting the level by hitting the refresh button in the upper right will also cause the collectible to disappear.
We are aware of this issue and are working on an update which will be available shortly.
In the meantime, the following procedure may help!
To get the item, enter the 15th level ("Ventilation Shaft") from the "Boiling Point" Level Select screen. The collectible should now be available (indicated by the "?" next to the duck meter).
To launch the 15th level ("Ventilation Shaft") from the Level Select screen (during gameplay):
1. Tap the Pause button in the upper right corner of the screen.
2. From the Pause menu, tap the Levels button.
3. Tap the Level 15 button.
4. The collectible item should now be available in the level.