Concerned with the quality of their tap water, growing numbers of Americans are drinking bottled water instead. Sales have increased from $276 million in 1976 to $1 billion in 1985, according to the International Bottled Water Association.

By law, bottled water must meet the same safe drinking water standards set by the Environmental Protection Agency for tap water. But while EPA has authority over tap water, the Food and Drug Administration enforces the standards for bottled water.

The exception is mineral water -- such as Perrier and Apollinaris -- which is exempt from federal drinking water standards. Such waters, which are expected to contain high levels of minerals, are subject to FDA standards for safety and wholesomeness.

But whether bottled water is better than tap water is a matter of debate.

"Under current quality standards, bottled water . . . is not guaranteed to be a safe and wholesome product," concluded a 1985 study by the California State Assembly Office of Research.

In California -- where one of every six residents drinks bottled water -- some "bottled water plants have been cited for 'doctoring' water samples with chlorine so that laboratory results would show no bacterial growth, for not monitoring the quality of their water sources or their product as required, for not keeping required records of water testing results, and for keeping false records which indicate more monitoring than is actually performed," the report said. In addition, the office noted levels of inorganic chemicals "which exceeded water standards" and the presence of organic chemicals, including benzene, phenols and chloroform.

The California study was done for "political motives," said William Deal, a spokesman for the International Bottled Water Association. "As a scientific study, many of those things cited were not factual, nor can they be substantiated. Under the new laws in California, bottled water is the most highly regulated drinking water source available to the consumer."

One thing is certain: At anywhere from 89 cents to $6 a gallon, bottled water costs at least 1,000 times as much as tap water, which averages 70 cents per 1,000 gallons.

To compare bottled and tap water, The Washington Post commissioned a laboratory analysis of one bottle each of six brands sold in area supermarkets. WaterTest Corp. in New Hampshire and Gascoyne Laboratories in Baltimore ran the same 51 water quality tests on the bottled water as they did on municipal drinking water samples.

Two striking results were contaminants found in Safeway brand spring water and Great Bear Salt and Chemical Free Water. Levels of the contaminants did not violate EPA standards.

In contrast to all other waters tested, Safeway brand spring water contained 0.060 milligrams per liter of dichlorodifluoromethane -- a chemical derivative of freon, the substance that helps cool refrigerators. EPA has set no standards for this chemical.

The Safeway spring water sold in this area comes from Seawright Spring in the Shenandoah Valley, said Cathy West, quality control supervisor for Safeway's Meat and Dairy Division, which also handles bottled water. The water is transported by tanker truck to the Safeway plant in Landover, Md., where it is bottled. Safeway does not treat the water at all, West said.

Safeway regularly runs tests on the water for bacterial counts, West said. Once a year, it is checked for the amount of metals present. But the company requires tests for organic chemicals (including dichlorodifluoromethane), she said, only "every five years. As for pesticides and herbicides, she said, "we don't test for those at all that I'm aware of."

Based on results of The Post's tests, Safeway spokesman Larry Johnson said that the company notifed the Maryland Health Department and will be conducting tests of its own.

On Thursday, Safeway took samples of their bottled water and sent them to Gascoyne Labrotatories for analysis. The tests, which were conducted on a different lot of bottled water from The Post's testing, "found no trace of anything," Safeway's Johnson said. "We think the water is in fine shape."

As a result of the Post findings, Johnson said that Safeway plans to do more frequent testing for organic chemicals.

Like all the tap water tested, Great Bear Salt and Chemical Free Water contained chloroform -- 0.021 milligrams per liter -- and chlorodibromomethane -- 0.010 milligrams per liter -- both chlorine byproducts known as trihalomethanes. These levels are within EPA standards.

The water "is processed from the Philadelphia municipal water system," said Robert Kelsey, Director of Quality Assurance for the Beatrice Co., parent company of Great Bear. The water goes through "a deionization process," Kelsey said, "but it will not remove all the contaminants that are in the water supply. It's designed to significantly reduce them."

The water also goes through carbon filtration to remove chlorine and "the majority of the trihalomethanes," he said. "But it depends on the municipal water system. We design our systems for an assumed amount coming in, but if they were to exceed the federal limits of 100 ppb [parts per billion, equivalent to 0.100 milligrams per liter], we would have trouble. I can tell you that these levels [of trihalomethanes] are on the high side for our product." One part per billion is equal to about eight drops of a contaminant in an Olympic-size swimming pool.

Asked why water labeled "chemical and salt free" would contain chloroform and dichlorobromomethane, Kelsey said: "I don't think I better answer that. It's a marketing decision, and I don't think that the marketing department would want to say 'essentially chemical and salt free.' " Enforcement of standards for bottled water is limited "by lack of enough inspectors," said Ray Gill, chief of the FDA's guidelines and compliance research branch, which monitors bottled water safety. "Obviously, when there is a limited number of inspectors, we can only get to a limited number of bottles of water."

In addition, Gill said, "we do not have the regulatory programs for testing bottled water for contaminants. But the history of the bottled water industry has been a good one."

The bottled water industry has also set up its own monitoring system that is "as strong or stronger than our inspection staff," Gill said. The International Bottled Water Association works with the National Sanitation Foundation in Ann Arbor, Mich., to do annual testing and inspecting of various bottled water companies, said IBWA's Deal. All bottled water producers tested by The Post are IBWA members.

Buying bottled water from an IBWA member company, Deal said, guarantees that the consumer is "given mandatory assurance going above and beyond what the EPA and the FDA require. The consumer has an assurance that the water they are using is safe."