“Water is everything,” observes Erin Brockovich (the real woman, not the Julia Roberts version), opening the new documentary from Oscar-winning filmmaker Jessica Yu (Breathing Lessons: The Life and Work of Mark O'Brien, SFIFF 1996). Last Call at the Oasis-inspired by Alex Prud'homme's book The Ripple Effect: The Fate of Fresh Water in the Twenty-First Century-offers interviews, sleek production values, and hard evidence to bolster an urgent message: The fresh, clean water that H2O-hogging Americans take for granted will not last forever. Moreover, the supply is both shrinking and being polluted faster than most of us realize. Experts chiming in alongside Brockovich include droll, deadpan UC Irvine hydrologist Jay Famiglietti and UC Berkeley biologist Tyrone Hayes, a frog expert who discovered that pesticides in the water were turning his male study subjects into hermaphrodites. Yu also highlights grassroots water activists, bottled-water opponents, and a PR firm trying to market eco-conscious recycled water to skeptical consumers (hint: get Jack Black to star in your ad campaign). Though most of the film concentrates on the United States-with a focus on thirsty places like Las Vegas-Last Call also travels to Australia's disastrously drought-affected cattle country. By the end of Yu's informative, surprisingly entertaining film, it's clear why she titled it Last Call, not Wake-Up Call. It's already too late for that.