From thundering pools to cocoa baths, the whirlpool tub is the most successful of bathroom designs. If ever there was an example of luxury derived from necessity it is the whirlpool bath. The best-known, of course, is the Jacuzzi, a brand name that has become generic - as Hoover has to the vacuum cleaner. As the Jacuzzi company says, the "idea of a relaxing soak in hot water is by no means a new one". Many have realised the benefits of immersing their bodies in hot water - from the Greeks, Romans, Vikings and Turks to Native American tribes and the Japanese.
Some baths were a little primitive and probably pretty uncomfortable, such as rough pools dug from the rocky lava of Iceland, where geothermally heated water bubbled to the surface. Others were highly sophisticated, including magnificent bath houses designed by the Romans - those in Bath in south west England among the most notable. The Romans (along with the Greeks and Egyptians) pioneered hydrotherapy techniques, using the waters to bring relief for sufferers of conditions such as arthritis or other rheumatic disorders.
Hundreds of years later, in 1956, the Jacuzzi family, descendants of seven Italian brothers who had emigrated to America in the early 1900s, followed in the pioneers' footsteps by inventing a home-hydrotherapy system to ease the suffering of one brother's arthritic son. They took an oversized bathtub and fitted it with pressure jets. The Jacuzzi brothers' expertise was in making machines; according to the Jacuzzi company's press material, they invented the first enclosed cabin monoplane, then agricultural pumps. It was with one of these pumps that they began the history of the Jacuzzi as we know it.
In 1968 Roy Jacuzzi, a third-generation family member, introduced the world to the "Roman bathtub", the first integrated whirlpool bath. The family patented the jets they had fitted into the tub (hence the registered Jacuzzi trademark) and produced a 50/50 air-to-water ratio providing a unique bathing experience. Medical practitioners seized upon the chance to use the spa baths to treat patients with hydrotherapy programmes but then necessity drifted into luxury as more and more people realised that, as well as soothing pain, these whirlpool baths felt rather terrific.
Hollywood got wind of the invention and the fabulous members of the movie jet-set were among the first private non-medical customers. Advertisements adorned billboards and magazines across America, showing lithe, tanned couples and families luxuriating in their bubbling tubs - and suddenly everybody wanted one. The whirlpool bath also introduced a significant change to society's habits and inhibitions. Rapidly it became acceptable (even enviable) to don a swimsuit and soak in proximity to other people, not in a public bath setting but in your own home.
Before they knew it, normally shy couples were up to their necks in bubbling water and steam and discussing policies and procedures with their boss or a Thanksgiving menu with the in-laws. Hundreds of thousands of Jacuzzis were installed and it became one of the most popular and successful bathroom design brands in the world. The company went on to diversify, introducing new designs such as the Avanza, a whirlpool bath that could be installed outside, and another called the Illusion, which had a central dome resembling a white volcano emerging from the water complete with in-built geysers. Most recently the company began offering an iPod docking station and audio systems on its models.
Albeit a pioneer in this design field, the Jacuzzi is now only one of many whirlpool or "spa" bath makers. Some have moved away from the boisterous jets fitted in earlier models, which pummelled the skin and - at full power - pushed smaller bathers around their baths. The Original Airbath, for example, spreads the power over more than 100 micro-jets rather than a handful of big thundering ones, allowing the entire body to be massaged evenly.
The bathroom manufacturer Kohler calmed the whirlpool bath concept down even further a few years ago when it produced a bath called the sok. The sok releases gentle streams of tiny bubbles and constantly overflows like an infinity pool, adding the sound of falling water to its relaxing properties. The sok is best enjoyed in conjunction with a phototherapy programme projecting a cycle of colours, each displayed for eight seconds, which is reputed to heal the body's tired and damaged organs.
London's Langham Hotel installed a sok in its Infinity Suite, which opened in 2005 and instantly became popular with Madonna and other A-list celebs. But I'm not sure what Madonna or the Jacuzzi brothers would make of the Whipped Cocoa Bath treatment at the Hotel Hershey in Pennsylvania in the United States. The 45-minute treatment using a whirlpool bath is, say its devotees, like sitting in a cup of warm, foaming cocoa. It harnesses aromatherapy and the benefits of a milk bath to soothe its chocoholic clients.
It all sounds deliciously decadent and something I feel sure that the Romans would have loved - if only they had thought of it first.