“A documentary and a three-alarm warning, “Flow” dives into our planet’s most essential resource — and third-largest industry — to find pollution, scarcity, human suffering and corporate profit. And that’s just in the United States.

Yet Irena Salina’s astonishingly wide-ranging film is less depressing than galvanizing, an informed and heartfelt examination of the tug of war between public health and private interests. From the dubious quality of our tap water (possibly laced with rocket fuel) to the terrifyingly unpoliced contents of bottled brands (one company pumped from the vicinity of a Superfund site), the movie ruthlessly dismantles our assumptions about water safety and government oversight.

Still reeling, we’re given a distressing glimpse of regions embroiled in bitter battles against privatization. In South Africa, villagers drink from stagnant ponds, unable to pay for the water that once was free, and protesters in Bolivia — where waste from a slaughterhouse is dumped into Lake Titicaca — brave gunfire to demand unrestricted access to potable water.”

There was one funny bit by Penn and Teller.