It was high summer in 1968 and Charles Hall was a 24-year-old graduate student at San Francisco State University. One hot afternoon he shut himself in his room and prepared to experiment with 300 pounds of liquid starch. But Hall was not a high-seeking hippie. He was a serious design student whose idea of a turn-on was pliant, yielding furniture that hugged its occupants in an embrace. So far, however, this was only a concept. He poured the 300 pounds of liquid starch into a vinyl bag and sat on it, but it was lumpy, cold, damp and decidedly unrapturous. Not to mention heavy. Next he tried reclining on blue-colored jelly inside transparent plastic. Ditto. And smelly with it.

Opting for simplicity, Hall poured plain tap water into a large, cushion-shaped vinyl pouch. The world quivered. He had invented the waterbed. It was a seminal moment in the history of slumber and a defining event for the Age of Aquarius. Soon the nights were alive with the sound of giggling and gurgling, as waterbeds became essential equipment among the lava lamps, the Ravi Shankar records and the illegal haze of marijuana. But their appeal was not just confined to those searching for a higher state of consciousness. Waterbeds transcended their status as a California novelty item to become an authentic social trend. Loaded with 2,000 pounds of water, and tons of sexual promise, they quickly spread through the emerging singles culture. Hugh Hefner, leading apostle of recreational pleasure, endorsed them . . . he ordered a king-size covered with the fur of Tasmanian opossum for the Playboy Mansion . . . and Bloomingdale's, leading arbiter of middle-class taste, stocked them as well. Wall Street brokers bought them, marriage counselors recommended them, hotels flaunted them.For many it was the perfect bed, both restful and sexy, although in the early days there were horror stories about floods, collapsing bedroom floors, seasickness and electrocution. Hall demonstrated the waterbed's durability by bouncing up and down on one on Dinah Shore's television show, and eventually it would become reliable and conventional enough to be installed in the Boeing 727 of Sheik Ahmed Zaki Yamani, Saudi Arabia's celebrated oil minister, and to become a standard accessory in the sleeping compartments of long-distance trucks.

Now, on its 30th anniversary, the evolved waterbed is sedate and almost suburban. It comes with a headboard these days, has adjustable surface tension, water temperature and wave action, and is firmly established in the tradition of mainstream sleep, trembling like blancmange in an estimated 35 million American homes. Sales, which peaked in the mid-'80s have been coasting along at a steady two million a year but have started to climb again, and what is now known as the "flotation sleep" industry is hoping that the current surge of nostalgia that has brought us films such as "Boogie Nights" and "The Ice Storm" (in which the waterbed plays a starring role) will carry it to another big boom.

Although it might give him a certain amount of satisfaction, Charles Hall does not care greatly whether the waterbed returns to the vanguard of fashion. He is a rich man, having got the courts to uphold his patent on waterbeds seven years ago. He still lives in California, in a house with three waterbeds, and reflects on a mission accomplished.

"I wanted to invent a bed that would replace the innerspring mattress," he says. "When a waterbed is adjusted right, the comfort is unsurpassed."

Fellow believers are preparing to celebrate three decades of sleeping on water this year, and the first anniversary salute has already been held in New Zealand, at one time the world leader in per capita waterbed use.

Hall never quite fitted in at San Francisco University. Tie-dyed, love-beaded and with flowers in its hair, the campus was the center of the counterculture. "But I was not a hippie," he says. While others tuned in and turned on, he fretted that "nobody was considering the comfort aspects of furniture . . . the form was way ahead of the function."

His comfy, cozy prototype waterbed was 8 feet square and 10 inches deep. "It was a combination of bed, lounging area and conversation piece, equipped with lighting, stereo and temperature control." He called it the Pleasure Pit, and when it was exhibited at a San Francisco gallery called The Cannery, it caused something of a sensation.

"It was a slow August news day," he says. "It made front pages all across the country."

Reworking the idea for the average bedroom, he and some backers started a company called Innerspace Environments to make and market the first waterbeds. They were ordered by members of Jefferson Airplane. One of the Smothers Brothers bought one. Elysian Fields, a Los Angeles nudist colony, took a truckload. Hall hired a Hollywood press agent who got them featured on television shows such as "I Love Lucy" and in movies.

The waterbed had arrived, and, predictably, other manufacturers quickly materialized.

"I got a vision," said Michael Zamoro, the most lyrical of Hall's early competitors. "I saw a wave of blue water like a breaker. And on the wave in golden script was written: "The World Wants Water-beds."

"People would just look at them and get erotic thoughts," says Hall. The timing was excellent. Everyone was being urged to look for more, better, ruder, louder sex. One manufacturer's ads promised: "Two things are better on a waterbed. One of them is sleep." "Live and love in liquid luxury," said another.

Salesmen assured buyers that their sex lives would be transformed because, as one explained: "The undulating mattress creates the impression that a third warm body is participating." Hotels rushed them into bridal suites.

For floor-dwelling hippies, the basic bed, essentially a water-filled vinyl balloon inside a sturdy wooden frame, had become a totem of the alternative lifestyle and they were shocked when gentrified versions . . . "capitalist rip-offs" as Rolling Stone was moved to describe them . . . started showing up in suburbia.

By 1971 they were in department stores coast to coast. In Washington, sales hit 7,500 a month and the waterbed showroom at Bloomingdale's in New York became a popular stop for cruising singles.

But back in California, the father of the waterbed wasn't sleeping too well. Innerspace Environments grew to 32 stores in California and had an advertising budget of more than $1 million, but the main beneficiaries of the waterbed boom were proving to be those at the low end of the market, the pony-tailed guys in the drug-culture stores who would fix you up with a no-frills bed for less than 50 bucks.

"The primitive hippie version was selling at the expense of our business while getting the benefit of all our publicity and advertising. We were marketing for a mature buyer. It didn't work." In 1973 Hall got out, selling his controlling interest in the business. Two years later, the company went bust.

Meanwhile, Lucille Ball and others who used the bed as a prop had inevitably focused on its supposed potential for mishap and slapstick. On the TV show "Phyllis," Cloris Leachman could be seen engulfed by the cascading contents of a pink, fur-covered waterbed she had contrived to lance with a letter opener.

"These shows didn't promote the product very well," says Hall. "There was always water squirting everywhere. In fact, the beds wouldn't squirt. There was no pressure."(He only knows of one confirmed fatality, and that was someone who managed to suffocate himself after getting trapped between the mattress and the frame.)

Eventually, however, the waterbed escaped both its hippie image and scary mythology. In 1975, the Journal of Property Management, no less, gave the waterbed its benediction, pronouncing it safe, and a nice little earner. "Waterbeds are here to stay,"' it said, noting that "the acceptance of waterbed tenants offers managers and owners another continuing opportunity to increase cash flow."

The approved waterbed now came in an infinite variety of styles . . . French provincial, Victorian, Scandinavian, Shaker. One model, the Grand Bahama, was a king-size four-poster with a mirrored canopy.

Besides their erotic properties, they were thought to have therapeutic value, too. The Whole Earth Catalogue, the manifesto of the counterculture, advised that when the last day of the world came, people should take their waterbed mattresses into the hills to make sure they got a good night's sleep before the end. Makers claimed that waterbed sleepers tossed and turned 60 percent less than users of traditional mattresses, and medical studies showed the waterbed's advantages for treating premature babies, narcotics-addicted infants, burn victims and arthritis sufferers.

Charles Hall was awarded a patent for "`liquid support for human bodies" in 1971, but in the freewheeling world of the early waterbed entrepreneurs, he rarely enforced it. "The industry was too young," he says. "These were people who just wanted to make some quick money to start a dope farm in Oregon."

But then in 1985, Intex Plastics, a major importer of waterbeds from Taiwan, sued to have the patent declared invalid. Hall sued right back, charging that Intex had infringed his patent on $50 million worth of beds, and in 1991 a jury awarded him $6.6 million. He has sold licenses to other companies for several million more.

"You can't fight the water," says Hall. "Sleeping on water is very natural. It's how you spent the first nine months of your life."