Back in 1954, Joe Jacuzzi and his brothers had no way of knowing their invention of a portable whirlpool pump would spawn a billion-dollar industry.

They simply sought to use hydrotherapy to ease the pain of a family member's rheumatoid arthritis.

Flash forward to 1998. Thanks to four decades of tinkering and testing, spa consumers now have the luxury of choosing a variety of high-tech options and features unimaginable 40 years ago.

Aside from the original concept of incorporating hot water and bubbles, no part of the spa's technology has gone unaltered. Inventors and entrepreneurs have changed the jets, surface, insulation, equipment and accessory items - even the product's name has undergone several permutations.

Bathing in the Bubbly

The original jacuzzi pump, when coupled with jets using an air-injection system, created a bubbly water-and-air mixture. As time progressed, a variety of manufacturers experimented with methods to propel the air/water stream into the spa.

At first. spas relied on a primitive bubbler concept that involved a vacuum cleaner-like motor operating in reverse, blowing air into the tub the way a child uses a straw to blow bubbles in milk. Injection systems came to depend on a sophisticated understanding of hydraulic principles.

Designers soon began speaking of things like the venturi principle, in which water is pumped through a funnel-like device to create a vacuum that pulls in air. As the water flow and pressure increase, the jet draws in more air, resulting in more water agitation.

"A venturi system is a conventional approach," said Roy Jacuzzi, chairman, CEO and president of Jacuzzi Inc. of Walnut Creek, Calif., and inventor of the first jetted bathtub. "What I did was take air and water all around that so I was getting a 300/60 air-to-water mixture.

"I was actually taking the water and air combination ... and exploding that," he added.

The earliest spas, though, incorporated only enough jets to churn the water.

"When we first came out with spas, they had two spa jets on them, said Bernie Burba, founder of Baja Products Ltd. in Tucson, Ariz. "Now you see portable spas with 60 on them.

"You might say that's overkill, but it isn't," he said. "We've really learned about water therapy and that lots of jets - lots of water and air moving across your body - is a very satisfying, restful and helpful experience."

Today, jets provide pulsating massage action all over the body, from stiff necks to ticklish toes. Spa makers now offer specific jets to caress shoulders, arms, wrists, thighs, knees, calves and ankles. At least one manufacturer, Bullfrog Spas, now boasts a system in which jet configurations can be interchanged throughout the spa, like the cushions of a couch.

Scratching the Surface

When the innovative spa builders sought out a more portable unit, they knew they needed a lightweight substitute for the gunite used for in-ground models. Manufacturers experimented with chopped glass, epoxy, resin and gelcoat. The advent of fiberglass altered the industry.

In the late '60s, a number of spa builders, including Len Gordon, Herb Quindt, James Kuehnle, and the crew at Marlin Fiberglass, all played a role in producing viable fiberglass molds. They coated the fiberglass with a gelcoat finish to make the surface less porous.

Builders applauded the introduction of fiberglass spas because these units, which cost less than their gunite counterparts, allowed for more uniform production. Spas could be mass-produced in molds, which provided greater consistency in the unit's hydraulics.

Fiberglass with a gelcoat finish, however, did not solve all of the builders' problems. Installing these units was difficult and before long, homeowners began complaining about "The Black Plague."

Spa owners across the country grumbled about the stubborn black stains appearing in their quickly dilapidating tubs, which faded in the sun, absorbed water and generally fell apart. Despite a flurry of explanations, no one had a definitive answer - or solution, kind the search for a new material was on.

In 1972, Baja Products, a manufacturer of acrylic-fiberglass diving board stands, introduced a vacuum-formed acrylic spa shell, which was reinforced with fiberglass.

"We started out by putting some in the harsh Arizona sun for a year and putting some others up in the upper Midwest where they had freezing climates to ensure that they would work before we started selling them," Burba said. "And those first ones really are still there, still working, and looking as good as when they were first put out."

Acrylic soon became the industry standard. Today, the major players in the acrylic industry, including Aristech Acrylics of Florence, Ky. and Cordova, Tenn.-based ICI Acrylics, continue to experiment with spa surfaces. The firms have modified the hot tub's colors and textures to create a fashionable though sturdy product.

While acrylic surfaces line the majority of portable spas, alternative polymer surfaces and soft-sided spas have also forged a niche in the marketplace.

Completely Equipped

Many of the first spa builders considered the units to be an offshoot of the pools they were accustomed to building. These builders delivered the hot water and bubbles using the products they had at hand.

While these jerry-rigged spas functioned adequately, they did not always fit the bill.

"The major problem with the portable was the limitation of use - as they were sold as a true portable that could be plugged into a 20-amp circuit," said Jim Brat, president of Brett Aqualine in Huntington Beach, Calif. "The problem was when you used them with the jets, the heater had to be turned off due to the higher amperage, and the spa temperature cooled off very quickly."

After dealing with heaters that burned out and pumps that overtaxed the system - coupled with increased competition - manufacturers began offering smaller, more compact equipment.

In the race to provide better equipment, Brett Aqualine introduced in 1977 what would later be termed the first "spa pack," an all-in-one component system that united the pump, heater, control, blower and plumbing.

Also at that time, Jeff and Jon Watkins formed Watkins Mfg. Corp. and built a self-contained and insulated portable spa. The company would later receive the industry's first UL listing for it's portable spa.

Electronic Evolution

Spa side controls brought the unit to the next technological level. The controls allowed the user to adjust the water temperature, circulation, jet action, air blower and spa light with the touch of a button.

Len Gordon, widely considered the "Father of the Spa Industry," engineered some of the first air-switch controls at his Las Vegas firm.

Bathers could adjust functions by pushing a button that sent short bursts of air through tubing running from the control panel to the spa machinery.

By 1982, innovative spa manufacturers incorporated high-tech electronics for portable spa use. Solid-state computerized systems and temperature-control devices entered the scene. Additional companies, providing custom-built controls for spa manufacturers, soon came on the market.

Two years later, Balboa Instruments, a Costa Mesa, Calif., electronic design and development firm, created an electronic switch suitable for use in the hot water industry.

Spa manufacturers considered these electronic controls, which featured solid-state components, more efficient and eye-catching than previous controls - and many hot tub makers incorporated them into their products.

With increasingly complex spa designs and options, these controls are helping reduce the impression that spas are too complicated, said Jacuzzi. "A lot of them now are becoming more consumer friendly.

Moving Forward

The advances in spa manufacturing spurred innovation in the accessory and water-care markets.

These products, which include the tapered spa cover, introduced to the industry in the '80s by San Marcos, Calif.-based Sunstar Enterprises, and chemical packages designed specifically for spa use, created a lucrative after-market.

Spas have come a long way since the introduction of the hydrotherapy tub in the '60s. Still, plenty of room for innovation remains. The quest for the ultimate insulation continues, and labor-free sanitation remains an elusive goal.

Today's hot tub retains hints of its history, while reveling in the possibilities of its future.

"Today, the spas that we have are absolutely unbelievable," Jacuzzi said.