Detailed guides to painful problems, treatments & more

Hydrotherapy, Water-Powered Rehab

A guide to using warm and cold water as a treatment for pain and injury

Paul Ingraham • 7m read
Vintage photo of a man in galvanic bath, seated on a chair between a pair of basins for his legs and a pair for his arms. There’s some old timey electrical hardware on the wall above him.

A galvanic bath, one of the quirkier old-timey hydrotherapies.

Hydrotherapy is an oddball assortment of ways to use water to relieve pain and assist rehabilitation from injury, mostly by heating and cooling. Methods range from conventional to kooky, and many seem quaint and old-school today, strongly associated with early physical therapy and the spa retreats that thrived about a century ago.

But hydrotherapy is far from dead — you’re doing it every time you have a hot bath or put an ice pack on a sprained ankle; strong full-body cryotherapy is trendy in sports right now; and many people have done injury rehab in a pool. Most people already practice simple hydrotherapies, and can upgrade with just a little education.

Why water?

Most hydrotherapy is thermoregulatory: it’s used to change our temperature, because water is a particularly handy way to heat and cool the human body.1 Manipulation of circulation, inflammation, and pain neurology with temperature are the most common goals of hydrotherapy.

But water is versatile stuff, and can be used in several other ways:

And there are several more medical uses of water, such as wound cleaning and burn treatment.

What’s better, hot or cold? Each one has its uses & it always comes down to personal preference. But in broad strokes, ice is for injuries & inflammation, while heat is for muscles, chronic pain & stress.

Is hydrotherapy effective?

There are so many forms of hydrotherapy that it’s impossible to generalize. They range from rank quackery to sensible mainstream medicine — each one has to be considered on its own merits. I get deeply into the science of heating and cooling in a series of several articles, as well as some of the other most popular hydrotherapies — lots of links at the bottom of this page.

I can safely say that most hydrotherapies are quite safe. They are also mostly simple, inexpensive, and are probably at least a little bit helpful because they are pleasant and even fun — and pleasant, fun things are inherently good for pain.2 No hydrotherapy is a miracle cure for anything, but it is a treatment approach that every chronic pain patient should have in their toolkit.

Helping out the body

The body is constantly trying to warm itself up and cool itself off. Sometimes it appreciates some help.

A lot of our physiological energy is devoted to the temperature balancing act.3 The whole system for temperature control is complex and amazingly effective. Unfortunately, it also isn’t perfect: we can’t always maintain an ideal temperature. We routinely use showers, baths, fires, fans, and even hot or cold foods to help with thermoregulation.

We struggle more with temperature control when we are sick or damaged, and so hydrotherapy is more helpful at those times. An obvious example is a cool bath when suffering from heat exhaustion. Hydrotherapy treatments that seem unremarkable when you are healthy can be surprisingly potent when your system is challenged by infection or fever.

Dog (Corgi) doing in a pool with a bright orange flotation vest and a human helper.

A Beagle enjoying (hopefully) a rehabilitative swim in hydrotherapy pool, wearing a flotation harness.

Taking the edge of inflammation

Easing inflammation in particular is another reason for the broad healing powers of hydrotherapy.

The process of inflammation always occurs with any injury — you know it by the pain, swelling, heat and redness. It is a normal response to any kind of tissue damage, and you couldn’t live without it. However, the body often over-reacts to trauma, sometimes quite dramatically,4 which can be painful and counterproductive. Inflammation can also be exaggerated everywhere by various factors.5 Just a little simple cooling for excessive inflammation can be a huge relief, and is much safer than over-the-counter pain medications (which have many notorious side effects). Warmth can also be soothing for diffuse low-grade inflammation.6

Unfortunately, many people still rush to put a hot pack on a fresh injury, especially a muscle strain. Except in a few special cases, this is an error. Never heat a fresh injury — you’ll make it worse, not better, because you will aggravate the inflammatory process, making it much more uncomfortable. And with some conditions, like back pain, it can be surprisingly unclear if the problem is an injury or not.

Moving blood around as a tonic

The stimulation and control of circulation is one of the main reasons that hydrotherapies may be healthful. The circulation of blood is the main way that the body regulates temperature. Therefore, it is possible to use hydrotherapy to manipulate and temporarily, significantly increase circulation.

The rate of flow of the blood determines the state of nutrition and the functioning of every cell in the body.

Frederick Erdman

Is circulatory stimulation beneficial by itself?7 No one really knows, but it probably constitutes a mild form of exercise — literally flexing countless peripheral blood vessels — and that’s especially beneficial if your ability to exercise is limited (by pain or injury, say).

About Paul Ingraham

Headshot of Paul Ingraham, short hair, neat beard, suit jacket.

I am a science writer in Vancouver, Canada. I was a Registered Massage Therapist for a decade and the assistant editor of for several years. I’ve had many injuries as a runner and ultimate player, and I’ve been a chronic pain patient myself since 2015. Full bio. See you on Facebook or Twitter., or subscribe:

Related Reading

Some hydrotherapy treatments to try …

Other related topics …

What’s new in this article?

2016 — Extensive upgrades and modernization.

Original publication date unknown, but probably before 2005. There have been a few unlogged minor updates over the years, but not many. It was a very rudimentary article for a long time.

2005 — Publication.


  1. Water has often been portrayed as “just a delivery system,” but in fact recent experiments suggest that “a substantial portion of the increase in skin blood flow associated with warm water therapy is probably associated with moisturizing of the skin rather than the heat itself” (Petrofsky et al) And so some hydrotherapies really may be about getting wet, and not just changing temperature.
  2. Pain by nature is powerfully tuned by unconscious perception of threat by the brain. This is much more than just placebo (though it does include placebo effects). See Pain is Weird.
  3. As compared to cold-blooded critters, which devote almost no biological resources to internal climate control, short of moving around. It’s a profound difference, two very different ways of being alive. Ours has great benefits, but it’s metabolically expensive.
  4. Ingraham. A Painful Biological Glitch that Causes Pointless Inflammation: How an evolutionary wrong turn led to a biological glitch that condemned the animal kingdom — you included — to much louder, longer pain.  ❐ 6608 words. Research has shown that immune cells (neutrophils) unnecessarily “swarm” sterile injury sites, causing damage and pain with no known or likely benefit as a tradeoff. It’s just a clear error: they appear to have mistaken mitochondria for a foreign organism, a legacy of ancient evolutionary history, and a biological glitch with profound implications about why some painful problems are so severe and stubborn.
  5. Chronic systemic inflammation can have many underlying causes, from bad genes to mild autoimmune disease (including allergies), smoking or other severe biological stresses, and even just getting old (which is known as “inflammaging,” see Franceschi et al). “Metabolic syndrome” is often the common denominator, a set of biological dysfunctions strongly linked to poor fitness, obesity, aging, and likely prolonged emotional stress and sleep disturbance as well (Gohil et al).
  6. Probably for entirely neurological reasons — that is, it’s not affecting the inflammation per se, just a pleasant sensory distraction.
  7. That is, increased circulation isolated from metabolic demand. Most large changes in circulation are driven by the need to deliver fuel to tissues during exercise. Adaptation to temperature changes also drives cardiovascular changes, but it may be much less pronounced.


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