About 10 years ago, Jay Famiglietti's colleagues at the University of Texas asked him to help remove some static on a satellite image of the Earth.

The UT geophysicists working with the Gravity Recovery and Climate Experiment satellites, an international program that includes NASA researchers, were finding huge changes in gravity that were not useful to their research.

It turned out those changes in gravity were caused by changes in fresh water, something Famiglietti, now a professor at the University of California at Irvine, has been researching ever since.

It is also the central point to "Last Call at the Oasis," a documentary being screened this morning and Thursday afternoon at the South by Southwest Film Conference and Festival.

The film looks at the issues of water quality and quantity, primarily in the United States, through personal stories and scientific research, producer Elise Pearlstein said.

Famiglietti's research is particularly important, she said, in explaining water quantity issues.

"Water is so heavy that when it moves, it affects the Earth's gravity," Famiglietti said.

So, as underground aquifers — primarily in the semiarid middle latitudes of the planet — emptied over time, the satellites picked up the changes in the Earth's weight.

Famiglietti said parts of the world are running out of groundwater because people are using it too quickly.

Water, of course, comes and goes with the seasons, so it's important to track changes over years, Famiglietti said. For example, if he sees an area where the annual low of groundwater availability is dropping, that points to depletion, Famiglietti said.

"It's a huge problem because most of that water we use to grow food, and humans need to do that," he said.

Researchers have been unable to determine how much groundwater is in the world. While Famiglietti's research shows how quickly humans use groundwater, there's still the unanswered question of how much the planet has left.

Not knowing that, Pearlstein said, makes it hard to plan how much water to use.

"It's pretty easy to overdraw your bank account if you don't see your balance," she said.

As for the water quality problem, Pearlstein said, the film shows how groups of people around the country hold industries and governmental agencies accountable for preserving water quality.

Contact Farzad Mashhood at 445-3972