Spa "cures" are among the most commonly prescribed treatments among Italian, French and German doctors. In Germany alone balneology - the technical name for water treatment - supports a pounds 9bn industry, much of it paid for by taxpayers.
For most of this century the British have declined to take part in the sybaritic pleasures of the water cure. Now, though, well heeled UK trend- setters are jostling to beat the Germans to the massage couches at a growing number of spa-cum-health-and-beauty centres in luxurious hotels. Thermalia Travel, which specialises in spa resorts, says the number of British clients has increased tenfold in five years.
The new fashion - like most - is actually a re-emergence of a very old one. The practice of bathing in and drinking from natural hot-water springs goes back nearly 3,000 years and countless ancient cities grew up around spas, including, of course, Bath itself. In the 17th and 18th centuries, "taking the waters" was de rigueur among England's gentry, but the practice declined with the rise of "rational" medicine, which offered instant, aggressive cures in place of slow, gentle ones.
In the rest of Europe, however, spas continued to flourish and many Continental doctors still think they are just as effective for many conditions as drugs and surgery. For chronic disorders such as persistent lower back pain, or gastrointestinal problems such as kidney stones, or liver and gall bladder complaints, spas are often used as a first line of treatment before more radical steps are taken.
The treatment has three central components: mineral water, massage and mud. The water may be bathed in, drunk or inhaled while massage can include aromatherapy, underwater jets, and various types of manipulation. Mud baths - known as fangotherapy - involve being covered in local clay that has been "matured" with bacteria and algae to create a biologically active and mineral-rich poultice.
Different spas are famous for treating different ailments, but nearly all of them claim to be good for rheumatism and arthritis; respiratory illnesses like asthma and bronchitis; skin conditions like eczema; circulation and digestive disorders and gynaecological complaints.
You can, of course, just roll up to your chosen spa and take a dip - most of the 5,000-odd springs in Europe are freely accessible. But a more systematic treatment is usually given in hotels and hospitals clustered around the water source. They vary from austere boarding houses staffed by stern nurses to magnificently luxurious hotels. Guests are given a check-up by a specialist balneologist and prescribed a treatment regime that typically involves a daily water or mud session, massage, rest and exercise. Some hotels provide a beauty, slimming, anti-stress or cellulite- busting package. Treatment styles range from the strictly remedial to the frankly hedonistic: one Turkish hotel invites guests to wallow in its massive indoor hot mineral bath while waiters hand out wine and sweetmeats and belly-dancers gyrate around the edge.
Spa treatments are undoubtedly beneficial. The warmth - most springs emerge at the temperature of a warm bath - eases stiffness, and the massage relaxes tight muscles. Combined with sun, exercise and good food - all important adjuncts - the feel-good factor is immense. But balneologists claim spa treatment does much more than create a sense of well-being.
Researchers at the University of Padua, for example, claim they can show that warm mineral water and mud has a wide range of specific effects. On the skin, they say it stimulates the underlying cells to produce new, healthy tissue, and when inhaled as steam it stimulates the immune cells in the mucous lining of the nose to put up stronger resistance to infections. They also say it reduces bronchial sensitivity - one study in France found that in asthmatic children who had spa therapy, the number of schooldays lost through illness was substantially reduced.
When the water is drunk, say the balneologists, it lowers blood cholesterol and triglyceride levels, and therefore may help to stop arteries from thickening. One study found people with severe cardiovascular disease were able to walk twice as far after spa therapy as before.
In the case of arthritic complaints, mud therapy has been shown to stimulate the metabolic activity which precedes cartilage regrowth. This, say the researchers, is one reason why 88 per cent of people with degenerative arthritis claim to be improved by the treatment.
Bone cell growth has also been shown to be stimulated, and it is thought that spa treatments could help people with osteoporosis. Fangotherapy has also been shown to stimulate production of anti-inflammatory hormones. Women with vaginal infections are said to benefit from the antiseptic action of the minerals, and the oestrogen found in some spa waters is said to help with menopausal symptoms. The mud reduces local water retention around the site of tissue damage, so it speeds recovery from surgery and sports injuries.
"Thermal treatments have been practised since antiquity but it is only recently that they have been systematically appraised," says Luciano Menozzi, professor of medical hydrology at the University of Padua. Research, he says "now gives hydrology a scientific basis like any other medical discipline."
Most British doctors are ignorant of or sceptical about these claims, but a small group have recently set up the British Association of Thermal Therapy (Bath) to investigate them.
"Obviously there's something to spa therapy, over and above the effects of water and relaxation," says Bath's chairman, Jeffrey Rosenberg, a London- based rheumatologist. "I have seen some very good results with psoriasis, but I reckon that 30 per cent or so is down to ultra-violet - sunlight; about the same amount is due to the minerals in the water and so on, and the rest is down to the psychological effect of a relaxing break."
Dr Colin Crosby, a sports medicine specialist in North London, puts the "feel-good" factor even higher, at about 70 per cent. "I wouldn't want to use spa therapy for acute injuries because - despite the anti-inflammatory claims made for the mud-baths - I suspect it would make things worse. But for arthritis caused by old injuries I think it could be very good," he says. "I have an old shoulder injury myself and last time I went to a spa I was given excellent physiotherapy alongside the water treatments. It certainly helped."
Dr Faith Haddad, a gynaecologist at the Garden Hospital, North London, and a member of Bath, is sceptical about some of the claims - that spa treatment can help with endometriosis, for example, or period pain. "I can see that the waters might be able to help vaginal infections" she says, "and any condition which is linked to stress could obviously be improved. But the main thing about it is that it is the most wonderful holiday you can imagine - and that has tremendous health benefits of its own."
Thermalia Travel arranges Spa holidays to Europe, Thailand and South Africa. A typical two-week package, including flights and treatments, costs about pounds 1,000. Telephone 0171-722 7218. Erna Low Consultants package deals include spas in Hungary and Switzerland.Telephone 0171-584 2841.