Thermal water isn't just tap water in a fancy bottle (or at least we hope it isn't). It's water distilled and bottled from hot springs, which are underground and are warmed by the Earth's geothermal activity. Bottled thermal spring water from companies like Avene, La Roche-Posay, Uriage and Vichy can range from $10 to $20 a bottle, and surprisingly, many people are ponying up, swearing by its benefits and myriad uses. So what's the secret?

Hot springs have long been thought to have therapeutic effects, with people bathing in them to help with all kinds of illnesses. In fact, in ancient Japanese culture, balneology is the treatment of many diseases using such baths. Their effectiveness is not clinically documented, though many swear by the benefits of soaking in a hot bath for relaxing, de-stressing, and perhaps therefore calming inflammatory responses of the body.

The thermal water from these hot springs has a much higher mineral content than regular water, although the mineral content of a specific brand is determined by where a particular thermal water originates. The minerals can include chlorides, sodium, selenium, potassium, calcium and magnesium. Different thermal waters boast the benefits of different minerals contained in their waters as well as the ratios of these minerals to each other. However, a high mineral content doesn't necessarily mean more benefit.

Science-backed benefits

A woman with a dab of skin cream that has thermal spring water ingredients Thermal water is often used an ingredient in skin care products. (Photo: Maryna Pleshkun/Shutterstock)

There have been a few studies measuring the benefits of thermal spring water, but they were largely conducted or paid for by the companies selling the water. Also, many of the studies are in vitro, which means that the water has been studied with cells or tissues in a controlled environment outside of a living organism. These studies are helpful, but they don't always indicate if product will be effective outside of a lab.

That being said, what kind of benefits did those studies find?

One study found that thermal waters protected cells from UV-related damage. The same study also found that a La Roche-Posay thermal water cream lessened the formation of sunburn cells in some people after exposure to UVB rays. The water also has been shown to have anti-inflammatory and even anti-carcinogenic properties.

This 2012 study tested thermal water's healing power on animal wounds and found that it had "regenerative properties" when it came to healing split skin.

The creams have been found to be helpful for some people in soothing the effects of eczema and psoriasis and reducing the appearance of scars. A 2010 study found that thermal spring water is "anti-irritant and, therefore, can be helpful to relieve skin irritation and in cosmetic formulations to improve the tolerability of the products."

But skincare experts concur that thermal water can be beneficial.

"I use Avene's thermal spring products daily in my work," explains Krisi Skinner, an aesthetician at Face Skincare in Bingham Farms, Michigan. "The balance of magnesium and calcium and low mineral content are extremely healing post laser procedure or post medical peel."

And lest you think thermal spring water is only for women concerned with their beauty regimen, it may be helpful for kids, too. Skinner says, "I think Avene Cicalfate Restorative Cream, which is high in thermal spring water, should be in every parents' medicine cabinet to help boo-boos heal post scrapes."