"Deep seawater" is a magic word that seems to make consumers believe any product made with it will be healthier and of higher quality.

Recently some TV programs and magazines have reported that deep seawater has dramatic power to improve your health, especially effective for such diseases as high blood pressure, menopausal disorders and atopic dermatitis. The impact of the mass media is tremendous. Sales of products made with deep seawater have skyrocketed since last year.

Among such products, bottled deep seawater has been a big hit. Umi no Shinsosui: Amami no Mizu, desalinated deep seawater bottled by Ako Kasei Co. in Kochi Prefecture, is now the second best-selling bottled water in Japan after Suntory's Minami Alps Tennensui.

Each 2-liter bottle is 700 yen to 800 yen, nearly triple the price of ordinary bottled water, but its healthy image stirs many health-obsessed consumers to buy it. The company produces 310,000 to 400,000 bottles a month, but the demand exceeds the supply.

Cosmetics using deep seawater are also popular. Cosmetic company Shu Uemura first launched Depsea Water skin freshener in 1998; so far about 1 million bottles have been sold. Depsea Water is basically desalinated seawater from Muroto, Kochi Prefecture, with natural herbal aroma compounds, and has "excellent moisture-keeping power, because deep seawater contains ingredients closely akin to human blood and body fluids," says Megumi Tatsuno of Shu Uemura.

Pleased with the success of the freshener, Shu Uemura has produced other cosmetics made with deep seawater since last year.

Few people know what deep seawater really is, however, or how it differs from ordinary water.

Deep seawater is taken from the depths of the ocean where the light of the sun does not reach -- usually deeper than 200 meters. It can be obtained from points where water is carried upward by currents or topological features of the sea bottom. Compared to surface water, it is cold, rich in nutrients and clean.

Unlike surface water, where plant plankton and algae consume inorganic nutrients necessary for sustained growth, deep seawater still has high levels of nitrates, silicates and phosphates. Also, deep seawater has less bacteria, and is not contaminated with chemical substances from the air and water outflow from rivers.

The first study of deep seawater was conducted in the 1920s by a French scientist who tried to generate electricity using the difference in temperature between the surface and deep seawater. More comprehensive studies, however, did not begin until the 1970s, after the oil shock.

In Japan, the nation's first research facility was built in 1989 at Cape Muroto in Kochi Prefecture, where 920 tons of water is pumped up from depths of 320 and 344 meters every day.

The water off Muroto is about 9 C all year around, 12 degrees lower than surface water, and it contains 10 to 30 times more minerals and 10 to 100 times less bacteria than the surface water.

In Kochi the deep seawater has been used for various purposes. The cultivation of fish and algae is especially commercially successful. Despite Kochi's warm climate, the water makes it possible to cultivate healthy fish and seaweeds that inhabit cold seas.

Many products using deep seawater have been developed by Kochi companies. At present 68 companies offer products including drinking water, other beverages, soy sauce, miso, salt, sake, noodles, sweets, tofu and bread. Buoyed by the nationwide "health boom," sales of those goods have been steadily increasing. Annual sales currently amount to nearly 4 billion yen.

The mass media have reported that those foods are healthier or tastier because of their higher mineral content, but that can be misleading, says Masayuki Takahashi, a University of Tokyo professor and author of the book "Umi ni Nemuru Shigen -- Kaiyo Shinsosui (Resources That Sleep in the Sea: Deep Seawater)."

To make it drinkable, for instance, seawater has to be desalinated. Usually salt is removed by the reverse osmosis system, filtering the water through a membrane, but this removes most minerals along with the sodium chloride, "so the collected water is almost the same as distilled water," Takahashi says.

Some makers blend a small amount of deep seawater with the desalinated water. One company insists that they remove only sodium chloride, and other minerals remain in their bottled water. According to an analysis by the Kochi Prefectural Industrial Technology Center, their bottled water contains more magnesium and calcium than ordinary bottled mineral water, but the percentage of the magnesium and calcium is only 15 percent to 17 percent of straight deep seawater, and many other substances were not found.

Still, there is merit in drinking bottled deep seawater. Takahashi says he drinks it "because it is clean. Tap water today is very dirty, and harmful chemicals cannot be removed by an ordinary water purifier."

He is skeptical about the widespread belief that deep seawater makes the taste of foods better. "I have tried sake made with deep seawater, but I do not find any remarkable difference," he says. "It may be because I don't have a keen enough sense of taste."

Mutsuo Hisatake of the Industrial Technology Center says minerals contained in the water can influence the taste and texture of food. In fermented foods and alcoholic beverages in particular, such minerals as magnesium and calcium activate the yeast and accelerate fermentation.

The correlation between the taste and the acceleration of fermentation has not been clear for many products, though, and "more research is needed," Hisatake says.

One rumor has it that deep seawater is effective for atopic dermatitis. A study by Kochi Medical School showed that it worked for 60 percent of patients who applied deep seawater to the affected areas. For some patients, however, it had a negative effect. How it affects the disease and why is unclear, and it will take years before the seawater can legally be used for medical treatment.

Takahashi feels that the image gets ahead of the reality. He emphasizes the utilization of deep seawater for food, cosmetics and medical purpose is unique to Japan, and it is "like an appetizer, not a main dish." The main purposes of the deep-sea project, he says, would be generating electric power, air conditioning, industrial cooling, cold-water agriculture and production of fishes and algae.

"Some people who see deep seawater as if it were medicine might start complaining that it doesn't work," Takahashi says. "I hope that doesn't discourage the deep seawater project itself. It is really a wonderful energy resource."