The simple chemical compound is drawn from the Potomac River near Watkins Island at 160 million turbulent gallons a day, 300 miles from its ancient source at the Fairfax Stone in western Maryland.

It is pushed through the Washington Suburban Sanitary Commission's filtration plant, in Potomac, by pumps that could fill a backyard pool in 30 seconds. It is cleaned in an hour and forced into 5,000 miles of pipeline at a velocity of five feet per second.

It is two hydrogen atoms sharing electrons with an atom of oxygen. A familiar, friendly commodity, routinely taken for granted before drought claimed the summer. A faithful, reliable, boring substance -- important, fundamentally, for the remarkable temperature range at which it stays liquid.

Yet it covers 70 percent of Earth, makes up 65 percent of each person -- 95 percent of each tomato -- and, on average, falls as precipitation in the amount of 4.2 trillion gallons on the United States every day.

Unfortunately, for the past several months or so, not enough of that rainfall has been here.

So it might bear recalling that water is amazing stuff. It tends to stick together. Bugs can walk on it. Fish can breathe it. In many places it is a symbol of spiritual cleansing.

The father of ancient Egypt's gods was Hapi, the deity of the Nile. The water of the Ganges is sacred in India. That of Lourdes, in France, is said to heal the afflicted.

But Noah barely survived it, and in extremes -- too much or too little -- it is awfully destructive.

And it has extremes.

Take rain.

Despite the current drought restrictions, Maryland has a town -- Unionville in Frederick County -- that holds the world record for seeing the most rainfall in one minute.

From 3:23 p.m. to 3:24 p.m. on July 4, 1956, a rain gauge -- operated by one G. Plitt von Eiff -- registered the fall of 1.23 inches of rain, according to Scott Stephens, a meteorologist with the National Climatic Data Center in Asheville, N.C.

"That's a lot of rain in just a minute," Stephens said. The area usually gets about 3.7 inches of rain in a month.

The world record for the most rain in a day is held by a locale called Foc-foc, on Reunion Island in the Indian Ocean 400 miles east of Madagascar. There, on Jan. 7 and 8, 1966, a tropical cyclone, aka hurricane, dumped 72 inches of rain.

Alvin, Tex., holds the U.S. record, set when tropical storm Claudette dropped 43 inches on July 25 and 26, 1979.

By contrast, the driest place in the United States is Death Valley, Calif., where the average yearly precipitation is 1.63 inches.

Bagdad -- the one that's now a California ghost town in the Mojave Desert -- holds the U.S. record for the longest dry period: 767 days, from 1912 to 1914.

The driest spot on Earth, Stephens said, appears to be Arica, Chile, which has an average yearly rainfall of 0.03 inches. Arica "holds a number of records," he said, the most stunning being that once it did not rain there for 14 years. Not a drop from 1903 to 1918.

"Basically, it doesn't rain there," he said. "Ever."

But when present, water has sculpted the Earth. It is sought by spacecraft on other planets as a possible cradle of life, and over the centuries, here and in other parts of the world, has been a force to be reckoned with by humans.

"It really does affect, every day, the decision making of every person on this planet," said Vern Scarborough, a professor of anthropology at the University of Cincinnati.

Water has been used as an object of cooperation, a weapon and a pawn in battle.

Caesar often sent his Roman legions after the enemy's water supply. The ancient Mesopotamian city-states of Lagash and Umma drew up history's most ancient recorded treaty after fighting, in part, over water.

Civilizations flourished and teetered over water. There is evidence of crude irrigation in southern Iraq 7,000 years ago.

In the United States, parts of the Great Plains were partly depopulated twice, in the 1890s and 1930s, over the lack of water. Even today, on the high plains of west Texas, the exotic art of cloud seeding to bring rain is a legitimate, growing, government-supported enterprise.

"Water is fickle," said Sandra Postel, a water scholar and director of the Water Policy Project, a conservation movement, in Amherst, Mass.

"We have an abundance of water on this planet, but it's not always available when we need it or where we need it. It lures us into thinking that it's an infinite kind of resource, that it's always going to be there. It creates the illusion of plenty."

The time in the United States where that illusion was shattered most cruelly was the Dust Bowl of the 1930s.

Fueled by a seven-year drought that started in 1931 and by dry, eroding topsoil, huge dust storms ravaged the plains for much of the mid-1930s.

The first storm tore through South Dakota on Armistice Day, Nov. 11, 1933, author Marc Reisner wrote in his 1986 book "Cadillac Desert," about the battle to water the American West.

The sky turned black. People vomited dirt. Jackrabbits went blind. Homeowners packed keyholes and windowsills with oiled cloth in a futile attempt to keep out the dust.

"A naked human tethered outside would have been rendered skinless -- such was the scouring power of the dirt-laden gales," Reisner wrote.

"The ravenous storms would blow for days at a time, eating the land in their path, lifting dust and dirt high enough to catch the jet stream, which carried it to Europe."

Tens of thousands of people departed on the epic Dust Bowl migration to California, denuding places such as Hall County, Tex., northeast of Lubbock, where the population dropped from 40,000 to 1,000.

Since then, the county's population has rebounded, but only to about 4,000, and the area around Lubbock remains serious about its water. So much so that it has become the cloud seeding capital of the nation.

Since olden times, people have been trying to coax rain from the clouds, having observed that rain seemed to follow on the heels of battles and fireworks.

In the 1890s, the Department of Agriculture funded experiments by a Maj. R.G. Dyrenforth, who used kites and balloons to loft explosives into the clouds above Midland, south of Lubbock.

A little rain fell, historians recount, but apparently not enough, for the good major came to be called "Dryhenceforth."

Today cloud seeders regularly work "rain enhancement programs" in the same area, using airplanes that fire rockets and flares containing silver iodide that state officials say has been shown to extract rain from clouds.

The silver iodide simulates an ice crystal, draws droplets of water like a magnet until it forms a full-fledged raindrop, which, along with others, then plummets to the North Texas plain as rainfall.

"Sometimes we can keep them going for an hour and a half," said A. Wayne Wyatt, the general manager of the High Plains Underground Water Conservation District 1, in Lubbock.

Alas, he added: "You've got to have clouds. You can't make it rain out of a clear sky."

Last week as Harold D. "Danny" Pendergraft, chief operator at the Potomac filtration plant, tended the mammoth facility under a cloudless sky, he noted that the Potomac was fed by arteries hundreds of miles away. "It's a reliable source for the Washington metropolitan area," he said.

And the river did seem placid as it flowed past the plant -- with an elegant, gray heron watching nearby -- except at the intake pipes where the water was dark and looked like it was boiling.