They called it "2 cents plain" on New York's lower East Side 40 years ago. Just water from the tap with an injection of CO2 to make it bubble. And it cost 2 cents. Unlike club soda it contains, no salt.

Some people never gave up drinking it (it was known as phosphates in other parts of the country), but for most Americans the only 2 cents plain they ever saw for several decades was mixed with scotch or bourbon.

The "plain's" fancy cousin made an enormous splash when it crossed the Atlantic several years ago and it suddenly became fashionable to drink salt-free sparkling water, especially if it was natural, had French name, came in a pale green bulbousshaped bottle and cost a lot of money.

Knowing a good thing when they saw one, manufacturers of other mineral waters entered the fray, but none of them has even come close to Perrier's cachet and popularity.

In a story on shifting food patterns, Travel & Leisure magazine noted that half of today's drink orders are for white wine and wondered if the other half are for Perrier. "Or," it asked, "are those even newer elixirs, low-salt seltzers and soda, washing out the bubbly imports?"

Could be. After all they cost less. And even Bruce Nevins, president of the company that imports Perrier, could not distinguish his own product from Canada Dry in the test. Nevins appeared on the Michael Jackson radio show in Los Angeles and was confronted with seven glasses of sparkling water. sAccording to Jackson, Nevins "picked out Perrier on his fifth guess."

A lot of people have come to the conclusion that if there is a noticeable difference in taste between the more expensive sparkling waters, both imported and domestic, and the seltzers it isn't worth the difference in price. There are some, like the man at the checkout counter last week who has started to hedge his bets. He had both Perrier and Vintage (a seltzer). "We drink the Perrier with lime and put Vintage in mixed drinks," he explained. "I don't know why. They probably don't taste any different."

Seltzer, sparkling water, club soda. The nomenclature is confusing and there is some overlap.

Seltzer is usually tap water that has been purified to remove the chlorine, tastes and ordors. Then it is charged with carbon dioxide, CO2. No salts are added.

Sparkling water has been carbonated with CO2. The water itself sometimes comes from a spring instead of the tap. Deer Park, Saratoga and LaNature are sparkling spring waters. Sparking waters have no added salts. There are also several other natural sparkling waters sold in this country: Perrier, Peters Val from West Germany, Ferarrelle from Italy and Portland Spring from Maine. The sparkle in these waters come out of the ground along with the water.

Club soda is purified, carbonated tap water with added salts.

Why are salts put in club soda?

According to Ed White, who bottles White Rock Sparking Mineral Water, salts are added to club soda "to enhance and retain carbonation." But the National Soft Drink Association, a trade association of bottlers and manufacturers, says that some people add salts "because they feel it makes a better product and adds flavor to whiskey" in mixed drinks.

Club soda have a high salt content compared to sparkling water and seltzer. It is much higher than the Environmental Protection Agency's recommended level for naturally occuring sodium in tap water -- 20 milligrams per litre which is a little more than a quart. A quart of Canada Dry Club Soda contains almost 200 mg.

The EPA recommended optimum limit is based on health considerations for those segments of the population who should restrict their intake of sodium because of hypertension. The level of naturally occuring sodium in seltzers and sparkling waters is determined by the level of sodium in the source. According to its producers, Vintage, bottled in Pennsylvania, has less than 10 milligrams per 7 ounce serving; Rock Creek, bottled here, has less than 3 mg in an 8 ounce serving.

The "Great American Health Kick" is also the reason for a renewed interest in salt-free drinks like seltzers. Perrier exploited this interest better than anyone else. But now sales are increasing for less expensive seltzers According to the president of Rock Creek Beverages, John Maynes, sales of Rock Creek Club Soda, which has no added salt so it could be called seltzer, are up "10 to 11 percent in the last five or six months, while sales of their traditional Blair House Club Soda have remained the same.

Giant can't keep Vintage in stock. Safeway began selling it last week, Vintage has been on the market for several years "in response to consumer demands. It has no additives, no chemicals, no sugar, no other things the government is cautioning us to stay away from," said a company spokesman.

"People are very concerned about salt in their diets," said Ed White of White Rock. "Now with the advent of concern about salt in water the seltzer water has made a comeback. We've taken the salt out of our club soda."

Until recently most of the demand for seltzer had been in the Philadelphia and New York markets. Today practically every supermarket chain in New York has a private label seltzer and Canada Dry is marketing seltzer in the Northeast. Washington may be on their list for expansion next year.

New York is the biggest market for seltzer in large part because of its sizable Jewish population. According to Edmond Rovner, a Bronx native, "Jews tended to drink seltzer in preference to bottled drinks. The seltzer was available in the local candy stores, the hub of every neighborhood. The New York candy store was the equivalent of the rural general store." It's still possible to have home delivery in New York of those old fashioned reusable seltzer bottles. They haven't been available for many years in Washington. You can, however, have a seltzer-making machine installed in your home for $1,500 or one attached to your refrigerator for $1,200. It also makes flavored sodas.

Or you can buy a Soda King, a soda syphon that turns ordinary tap water into seltzer with the aid of cartridges filled with CO2. Several stores in town carry them, including Kitchen Bazaar where they sell for $19.99 and Rodman's where the price is $15.99. Bar Mart sells Soda Master which comes in several models that range in price from $29.50 to $50.

However you buy it, "2 cents plain" seems to be here to stay. It would have made Harry Golden very happy.

The accompanying chart indicates the sodium content and the cost of some sparkling waters, seltzers and club soda s available in Washington area supermarkets. Information on sodium content is either from the manufacturers or is listed on the bottle. Prices vary.