Last Call At The Oasis looks at the very real threat of a water shortage in the United States, with documentary-maker Jessica Yu receiving insight on the issue from figures ranging from clean-water crusader Erin Brockovich to comedian Jack Black.

Despite the funnyman's appearance, however, the subject of the film is no laughing matter, according to the Academy Award-winning director. She says most North Americans do not appreciate the severity of the water supply situation in this part of the world.

As her film screens at the Toronto International Film Festival, Yu spoke with CBC News about the issues surrounding water shortage and what she hopes audiences will take away from the movie.