The Complete Guide to Natural Geothermal Hot Springs: Why Mineral Content Matters

“Hot springs” is a term that gets stretched. Some resorts use actual geothermal water pulled from deep volcanic aquifers, while others heat tap water and add minerals. The experience might look similar from the outside, but the therapeutic potential isn’t.

This guide breaks down what makes water naturally geothermal, what the research shows about mineral-water balneotherapy, and what to actually look for when choosing a resort.

What Makes Water “Naturally Geothermal”?

Natural geothermal water rises from deep volcanic aquifers, carrying dissolved minerals accumulated through long contact with surrounding rock layers, creating water that is chemically distinct from typical surface or municipal water sources.

This is the basis of balneotherapy: the therapeutic use of natural mineral waters. According to the Global Wellness Institute, the practice spans more than 4,000 years and is practiced across cultures worldwide. Today, the thermal and mineral springs sector is valued at roughly $60–70 billion, with tens of thousands of facilities operating across more than 100 countries.

By contrast, heated mineral pools work differently. The water is warmed mechanically, typically from tap or municipal sources, and some operators add mineral compounds to approximate natural spring water. While pleasant, these experiences don’t replicate what actually happens geologically.

The Science Behind Soaking: What Balneotherapy Research Shows

The science points to a consistent conclusion: minerals in natural geothermal water appear to work alongside heat, buoyancy, and hydrostatic pressure, not just alongside them. 

Researchers at Sapienza University of Rome documented this dual mechanism: physical properties of water (temperature, pressure, buoyancy) combined with the direct chemical action of dissolved mineral compounds on the skin and underlying tissues.

Murrieta Hot Springs Resort draws its 49+ soaking pools exclusively from 100% natural geothermal sources, with no water heating or mineral supplementation.

The Nine Minerals in Natural Geothermal Water (and Why Each One Matters)

No two springs carry the same mineral profile, the composition reflects the specific geology of the aquifer the water travels through. The following are the nine minerals documented at Murrieta Hot Springs Resort:

A few minerals worth highlighting specifically: 

•  Calcium: linked to improved bone mineral density, particularly in postmenopausal women

•  Magnesium: supports nerve function and blood pressure regulation and is commonly present in mineral spring waters in combination with sulfate

•  Silica: associated with skin elasticity and reduced visible aging

•  Bicarbonate: helps regulate digestive acid levels and supports systemic pH balance

The key consideration is bioavailability. When these minerals are present in their natural dissolved ionic form, as they exist in true geothermal water, the body may interact with them differently than it would from isolated supplements or artificially fortified water.

Natural Geothermal vs. Heated Mineral Pools: A Practical Comparison

When a resort markets itself as a “hot springs” experience, the nature of the water determines whether a soak carries the potential benefits associated with mineral-water balneotherapy, or just the relaxation benefits of warm water.

What to Look for When Choosing a Hot Springs Resort

Before booking, ask is the water actually geothermal? How a resort answers that question, and how transparent they are about it, tells guests almost everything they need to know.

Beyond water authenticity, here is a practical checklist for evaluating a hot springs destination:

Why Murrieta Hot Springs Resort Is the Natural Choice in Southern California

Between Los Angeles and San Diego region, Murrieta Hot Springs Resort is the only natural geothermal hot springs resort that offers overnight accommodations, and its water is 100% geothermal with no mechanical heating or mineral supplementation.

•  49+ soaking pools: the largest collection of natural geothermal soaking pools in Southern California

•  9 verified therapeutic minerals: Sulfate, Chloride, Boron, Calcium, Lithium, Potassium, Sodium, Silica, and Bicarbonate

•  24-hour unlimited soaking access for overnight guests: the kind of extended immersion balneotherapy research ties to meaningful outcomes

•  Medical overnight: wellness programming directed by Medical Director Dr. Marcus Coplin and VP of Wellness Sharon Holtz

USA TODAY’s 10Best named Murrieta Hot Springs Resort the #2 Best Spa Resort in the USA and #3 Best Hot Springs in the USA in 2025.