PAYING for bottled water is like paying for air, huff those who favor the faucet. Why should you pay for it when you can breathe it for free?

Perhaps. Yet thousands of Americans, apparently as finicky about the taste of their water as the French are about wine, are expected to plop down $200 million this year for bottled water they could otherwise secure from the tap for a pittance. Of course, in matters of aqua , the French and their European neighbors have been persnickety for ages. Even Charlemagne is said to have bubbled over at the prospect of a good hot bath and a double mineral water, straight up, at the neighborhood spa.

On this continent, though, the recent love affair with effervescent Perrier is no secret, and the bottled-water industry claims an ever-growing flirtation, at the rate of 10 to 12 percent a year, between no-fizz spring waters and the lips of America.

Not that there is anything bacilllary swimming around in our tap water that a heavy dose of chlorine won't kill; it's just that some folks prefer savoring their tea and coffee without the chemical. In matters of such importance, taste seems the vital thing.

Others are simply convinced - in spite of municipal government protestations of studies condemning their public water supplies - that drinking tap water makes the health gods fidget.

All this commotion over water - to pay or not to pay for what you can get virtually free - makes the folks who dispense the stuff in bottles highly pleased, and they dispatch burly watermen like Raymond Nivens, 53, into the world to lug about 55-pound, five-gallon jugs. The other morning, as is his and his colleagues' wont most days, Nivens was hoisting water bottles all over town from a 1976 Chevy Step Van, breaking his back to slake the growing thirst of people who say "phooey" to tap water.

Nivens parks the truck, grunts a five-gallon glass jug to his shoulder and trudges into a construction office on upper Connecticut Avenue. It's the first call this one-man oasis on-the-hoof will pay on grocery stores, health boutiques, offices and homes this day, and he pauses briefly to sip the sweet nactar of reminiscence.

"I used to take Mountain Valley water to Sam Rayburn," he says. "Lots of senators drink it. I went up to Adam Clayton Powell's office all the time before he left town, and even delivered to Mrs. [Marjorie Merri-weather] post before she died."

One day, on the way to her refrigerator, in fact, Raymond Nivens ran smack into the multimillionarie doyenne. "She was very nice to me. She spoke a few casual words and that was when I noticed she didn't look her age at all. She was in her 80s and looked 45. Who knows? Maybe it was the water."

Sen. Strom Thurmond drinkd it.

Frank Sinatra sells it.

Raymond Nivens delivers it.

Up goes the jug. Nivens trudges up steps and disappears into a trailer at the construction site, where he meets the day's first Doubting Thomas. As he vanishes out of earshot to refill the cooler, Superintendent Dick Ashley, 22, snickers over the boss' taste for bottled water.

"I fill it up every day with tap water. No one notices the difference except the boss. At home, I use well water. It's the dirtiest water in the world. I brush my teeth with it, drink it, shower in it . . . and I feel ifne."

Nivens trundles back to request $8.93 before he installs the new jug of Mountain Valley - a popular, if expensive, domestic water that gurgles up in Hot Springs, Arkansas. There, back in 1541, the story goes, explorer Hernando de Soto stumbled upon the spring and, to the delight of company historians, found a number of fierce warriors from hostile tribes lolling about peaceably, recuperating beside the still waters. In the 1930s, the baths earned a quiet reputation as a sort of mobsters' DMZ, where rival gangland chiefs from the east could drop their towels sans fear.

But on this day, four centuries later, the water promotes only trouble. No money, no Mountain Valley, says Nivens.

The construction man pokes in his wallet - it's empty. "Why do we have to pay for water?" asks Ashley. "You can go out to River Road and get free spring water anytime . . ."

"That water's got bacteria in it," says Nivens," But this water's pure, crystal clear. This water is the best water in America!"

Ashley smirks, points to the counterfeit bottle and instructs the waterman fo fill a cup - and drink. "Taste it! Taste it!"

The waterman's Adam's apple bobs once, twice . . .

"This ain't Mountain Valley. This is city water!" cries the waterman. He looks as if he just might spit it on the floor, but swallows hard - GLUG! - like a good sport, and heads for the truck.

"How could you tell the difference?" he is asked.

"You just can. My customers run out, they'd rather die of thirst than drink from the tap."

IF SOME delivery men complain that they barely glimpse life through the back door, Raymond Nivens is exuberant about his lot. He feels he's part of history on the march.

He delivers the lightly saline Vichy, from Julius Caesar's favorite spa in the heart of France, to $500,000 homes in Georgetown.At the derriere of the French embassy, he waves au revoir to cases of Evian, Contrexeville and Perrier. Bottles of Apollinaris, from the resort of Bad Neuenahr in Germany's Ahr Valley, are earmarked for the Germans.

And at the Italian embassy, well, it's arrivederci , Fiuggi, a clear, noncarbonated water from springs near the Sacco River in central Italy. A water that not only made the popes smile, claims the company, but dissolved Michelangelo's kidney stones.

As for Mountain Valley, it jets along to foreign lands aborad Air Force One - to safeguard the President from Montezuma's Revenge, Delhi Belly or New Caledonia Catarrh. "We've delivered to the White House ever since Calvin Coolidge," says Mountain Valley president John Scott. "He was a tightwad, but at least he bought water."

Most of the home-delivered, high-priced water hereabouts goes to Georgetown, Chevy Chase, Bethesda, Potomac, McLean, Alexandria or Cleveland Park, to people like Jim Conaway, 37, a novelist, and his wife, Penny, who accepted their inaugural jug the other day.

Conaway, like so many members of the Nat-u-ral Generation, distrusts junk food and tap water. After reading news reports that local water supplies contained possible carcinogens from chlorine combining with organic material in the water, he reached for the phone. His daughters are enthralled over pushing the jug's pump.

But there are poor folks who buy it, too, like the elderly woman who leans on a cane at the top of the stairs in her 13th Street NW home and beseeches Raymond Nivens, "Please, mister, don't turn off my ster!" But it is only after she puts on her glasses that she realizes he is from the other water company. "I am so glad you brought my water," she says. "But it sure is expensive; I got to mix what's in the bottle with wate from my faucet to make it last."

She has yet to discover the proliferation of budget waters like Deer Park (49 cents a gallon) that have come to lately jump off the shelves at grocery stores.

Safeway says there is no typical customer who buys the four brands they carry. Bottled water buyers are now old and young, rich and poor, cantankerous and genteel, the middle class.

WILL THE WATERMAN someday replace the proverbial milkman? That's anybody's guess.

In Southern California, America's fountain of fad, more people drink bottled wate than anywhere else in the country, with two out of every seven plopping down $80 million a year for the privilege.

But elsewhere, too, America has gone organic. A 1976 Harris Poll found that food health was the top priority among Americans, regardless of age, education or income. Only a handful believed they ate the kinds of foods needed to stay chipper, and almost half felt they would be well served to cut down on salt, sugar, soft drinks - junkfood.

Last year, the Natural Generation was gobbling $1 billion worth of "health food," up from a paltry $60 million a decade back. And among the new disciples of Euell Gibbons are those who gag at the mer thought of drinking tap water.

Some are splashing mad over studies suggesting that, even after purification in municipal water plants, possible cancer-causing substances remain in public water supplies across the land. Whether or not bottled water is, in fact, any safer, a lot of consumers believe it is. Ergo, the changing tastes of America have drawn such companies as Borden's into the bottled-water market in the East," with local sales of Polar Water, the Borden brand, leap-frogging at the rate of 30 to 35 per cent a year, compared to 25 percent for the division as a whole.

A recent Borden's market study suggests that consumers who can afford it buy distilled or spring water because they prefer it on the tongue, rather than from fear of what may lurk in the public pool. "The public may be disturbed about tap water, but if they can't afford bottled water, they tolerate it," says Conte.

Polar Water gushes from a spring in Manheim, Pa., where it is treated with ozone to kill bacteria, bottled and sent on its way to homes, drug stores and area supermarkets. At $2.75 for five gallons, or about 79 cents a gallon, it's among the numerous brands of domestic spring water that cost less than half the price of Mountain Valley, and considerably less again than European imports. Polar (and competitors like Great Bear, which is basically a purified tap water) isn't snooty water. "We appeal to the masses," says Conte.

And every time the faucet runneth muddy, their phone ringeth off the hook. "Our biggest competitor is tap water," he says.

MOUNTAIN VALLEY!" Raymond Nivens knocks twice.

"Just a minute," yells an old lady from behind her apartment door. Now comes a rustle of papers and boxes, the unclicking of locks and latches. A thin, white-haired woman in a blue robe hobbles out.

She has been pacing about, watching the clock, she says. It was past time for her medicine, and she wanted her chaser. "I never take my pills with city water," she says.

Nothing puts a grin on the face like the waterman at the door with a fresh jug of H.O. In the winter, customers warm Nivens with steamy cups of coffee. In the summer, they quench his thirst with iced tea or lemonade. (Of course, such refreshment is never made with - yech! - tap water.) And this day, so pleased is retired Admiral Charles Owen Comp, 79, whose flagship lodged President Roosevelt at Yalta, that he slips Nivens a $1 tip. "We tried drinking city water," he says. "But there were just too many polliwogs in it."

On down Connecticut Avenue. Claiming his turf, the waterman waves at liquor stores, drug stores, hotels, apartments. He nods toward a passing window. Up there lives an old man who has been sick for the longest time. On down the road, a nes customer confides she has just learned that she has cancer and wants to take every precaution.

Deliveries to the infirm make the waterman feel like a saint, but he takes their "miracles" in stride. As for the woman who swore bottled water cured her arthritis, well, Nivens would only say this: "Last time I saw her, she was walkin' pretty good."