Okay, bathe the kids, put them to bed, make the last trip up the stairs to dispense the requisite last drink of water, and then settle in with an on-the-rocks beverage of your own to watch ABC News shatter your last illusions about the safety of your world.

It's the water.

From Long Island to San Jose. From the grease-and-grime cities of the Northeast to the squeaky-clean silicon valleys of California. There's stuff in the water and it's getting worse.

Four years after it aired "The Killing Ground," its award-winning documentary on hazardous waste dumping, ABC's "Closeup" strikes again. "Water--A Clear and Present Danger," at 10 tonight on Channel 7, is a disturbing hour-long look at the unnatural consequences of decades of careless handling of manmade poisons. The underground aquifers that supply drinking water for more than half the nation's populace are becoming contaminated at an alarming rate.

The abundant water resources that sustain our lives, "Closeup" reports, are becoming "a threat to life itself."

Scary? You bet.

* In the great Central Valley of California, the water under more than 7,000 square miles from Lodi to Bakersfield is contaminated with a pesticide called DBCP. DBCP, once used to sterilize root pests, does the same to people. It also causes cancer in laboratory animals. More than a million Californians get their drinking water from Central Valley aquifers.

More than 35,000 pesticides are in use in the United States, "made to destroy life we don't want," host Marshall Frady reports. "Now we are drinking them."

* In south San Jose, solvents from Southern California's high-tech computer industry have leached into the water system of a major urban area. A lawyer for a citizens' group tracks its progress on a neighborhood map stuck with pins and flags. Blue for miscarriage, red for heart disease, yellow for cancer, black for death.

* In Woburn, Mass., where solvents from buried hazardous wastes have leached into the water supply, a young mother who lost a son to leukemia watches her surviving son cross the street and wonders aloud, "Where are they going to live that's safe and clean? What water are they going to drink?"

The biggest problem in filming a documentary on the hazards of ground water contamination is, of course, filming the ground water. On that basis, ABC might be forgiven the endless footage of river rapids, bubbling streams, serene lakes and dripping icicles it uses to illustrate this pervasive but essentially nontelegenic environmental problem.

Less forgivable is the occasionally overblown rhetoric ("A flood of chemicals has invaded America's drinking water," intones Frady in the show's introduction, over the roar of falling water).

And in at least one instance the "Closeup" team balances precariously on the verge of hype. "Closeup" reports that an Environmental Protection Agency study found 5 1/2 million rural families were drinking contaminated water. True enough, except that much of that contamination was in the form of coliform bacteria--sewage, in other words--not toxic chemical residues, as all that precedes would lead the viewer to believe.

Despite its defects, "Water" is a visually powerful and legitimately frightening report.

A concerned citizen sums it up on film: "I'm told that I'm supposed to fear communists and sophisticated weaponry--and our more immediate danger is here . . ."