Do Hot Springs Resorts Add Chlorine? How Natural Mineral Pools Are Maintained

It is one of the most common questions guests ask before booking, and one of the hardest to get a straight answer to: is the water in a hot springs pool chlorinated?

The honest answer is that it depends on the pool, not the resort. At many geothermal properties, some pools are chemically treated and others are not, for reasons that come down to how the water moves and what state regulation requires.

This guide explains how natural mineral pools are actually maintained, when disinfection is required in California, and how to find out what you are soaking in before you arrive.

Three Ways Hot Springs Pools Are Maintained

The first method is the one guests picture when they imagine a hot spring, and it is only possible when a property has a live geothermal source producing enough volume to keep water moving continuously.

Why Flowthrough Pools Do Not Need Additives

A conventional pool holds the same water for weeks or months. Anything introduced into it stays until it is filtered out or chemically neutralized, which is why continuous disinfection is required.

A flowthrough mineral pool works on a different principle. Water arrives from the source, passes through the soaking basin, and exits. Rather than treating a static volume, the pool is continually replaced with fresh mineral water. Cleanliness comes from turnover, not chemistry.

This also preserves the water’s mineral composition. Naturally geothermal water carries dissolved minerals accumulated through long contact with subsurface rock, and adding chemical treatment changes what is in the water. Flowthrough keeps the source profile intact, which is the entire point of soaking in geothermal water rather than a heated pool.

What California Regulation Requires

California treats commercial soaking pools as public pools, and public pools must be continuously disinfected with a measurable residual. Under the state’s public pool standards, free chlorine residual for public pools must fall between 1.0 and 10.0 parts per million, with a higher minimum for spas.

Mineral springs pools are handled differently. State regulation includes a fresh water flow exception: mineral springs pools that meet the flow standard set in the California Building Code must comply with all other public pool requirements but are not subject to the continuous disinfection requirement, provided monthly bacteriological water quality standards are met. Mineral springs pools that do not meet that flow standard must be disinfected like any other public pool.

In plain terms: if enough fresh mineral water flows through a pool, and the water tests clean on an ongoing basis, chemical disinfection is not required. If it does not, it is.

That single rule explains why a hot springs resort can honestly say some of its pools are untreated while others are chlorinated. Both statements are true at the same property, for different pools.

How Murrieta Hot Springs Resort Handles It

Murrieta Hot Springs Resort draws all of its water from 100% natural geothermal mineral water rising through the 46-acre property, carrying nine naturally occurring minerals: sulfate, chloride, boron, calcium, lithium, potassium, sodium, silica, and bicarbonate.

• More than 20 pools operate on natural flowthrough. These are managed hygienically to maintain the integrity of the water and its natural flow, and no additives are needed.
• Certain pools are chlorinated to meet state standards. This applies to the Roman Spa, the adults-only pools, the family-friendly pools, and the Historic Bathhouse water, where chlorination is used to ensure compliance with California requirements.

We publish this because guests deserve to know which is which. A resort claiming that every pool on a large property is entirely untreated is either misdescribing its operation or operating outside the rules.

With 49+ soaking pools, the largest collection of natural geothermal pools in Southern California, guests who specifically want untreated flowthrough soaking have more than 20 options to choose from.

Does Chlorine Change the Benefits of Mineral Water?

Chlorination does not remove the dissolved minerals in geothermal water. Sulfate, silica, calcium, bicarbonate, and the rest remain present in a treated mineral pool.

What changes is the character of the water. Guests often describe treated pools as feeling slightly different on the skin, and the chemical scent is noticeable to some. The heat, buoyancy, and hydrostatic pressure that drive much of the therapeutic response to thermal bathing are unaffected.

Research on balneotherapy points to a combined mechanism: the physical properties of warm water immersion working alongside the chemical action of dissolved minerals. Both are present in a chlorinated geothermal pool. For guests who want the water exactly as it emerges, flowthrough pools are the ones to seek out.

How to Find Out Before You Book

Ask these directly. Any property that manages its water well will answer without hesitation.

• Which pools use flowthrough, and which recirculate? This is the question that actually determines chemical treatment.
• Is the source water geothermal, or heated? Heated municipal water is always treated, without exception.
• How often is water quality tested? Untreated mineral pools are subject to regular bacteriological testing requirements.
• Are minerals naturally occurring or added? Properties with real geothermal water publish their mineral profile.
• Can I see the pool map? Properties that are transparent about water handling generally document their pools individually.

A vague answer to a specific question is worth noting. “Our water is all natural” is marketing language, not an operational description.

FAQs

Do all hot springs resorts use chlorine?

No. Resorts with sufficient natural flow can operate soaking pools without chemical disinfection, subject to water quality testing. Many properties run a mix, with untreated flowthrough pools alongside chlorinated pools that do not meet the flow standard.

Is chlorinated mineral water still mineral water?

Yes. Disinfection does not strip out dissolved minerals. The mineral profile of the source water remains, though the water’s feel and scent change.

How can I tell if a pool is chlorinated?

Smell is the most reliable everyday cue, though it is not definitive since some mineral waters carry a sulfur odor of their own. The dependable approach is to ask the resort directly which pools use flowthrough and which are treated.

Are untreated hot springs pools safe?

Pools operating under the flow exception are still regulated. They must meet all other public pool standards and satisfy ongoing bacteriological water quality testing. The exception applies to continuous chemical disinfection, not to oversight.

Which pools at Murrieta Hot Springs Resort are untreated?

More than 20 pools operate on pure geothermal flowthrough with no additives. The Roman Spa, adults-only pools, family-friendly pools, and Historic Bathhouse are chlorinated for state compliance. Details on individual pools are available on our .

To plan a visit to Murrieta Hot Springs Resort, visit murrieta-hotsprings.com.