Hydrotherapy Glossary: Terms in Plain Language
Plain-language meanings for the water, temperature, safety and spa terms used across the hydrotherapy library, with links to the page that explains each in depth.
Content last updated . This page has not been medically reviewed.
How to Use This Glossary
Hydrotherapy words are used loosely, and the same word can mean different things in a spa brochure, a hospital and a research paper. This page gives short, plain meanings and points to the page that goes deeper. Nothing here is medical advice, and no practice in this library is a cure or a prevention for any disease. Start with What Is Hydrotherapy? if you are new to the topic.Core Terms
| Term | Plain meaning | Read more |
|---|---|---|
| Hydrotherapy | One international proposal uses this word for therapy with plain tap water. [1] In rehabilitation research it is often used for exercise in water. | More about Hydrotherapy → |
| Balneotherapy | The same proposal uses this word for therapy with natural mineral waters, gases and peloids (a term for medical muds). [1] | More about Balneotherapy → |
| Spa therapy | Treatment or a visit built around water at a spa or health resort; the linked page compares it with the other terms. | More about Spa therapy → |
| Aquatic exercise | Exercise done in a pool, such as water aerobics. | More about Aquatic exercise → |
| Aquatic physical therapy | Rehabilitation delivered in a pool by a trained therapist. | More about Aquatic physical therapy → |
| Sitz bath | Sitting in a shallow bath of water, often used for the bottom and hips. | More about Sitz bath → |
| Contrast bathing | Alternating warmer and cooler water. | More about Contrast bathing → |
| Hot tub or whirlpool | A heated tub for sitting in, often with jets. | More about Hot tub or whirlpool → |
The proposal's own authors note that the field lacks internationally accepted terms. [1] That is why two sources can use the same word differently.
Body and Water Terms
| Term | Plain meaning | Read more |
|---|---|---|
| Buoyancy | The upward push of water that makes the body feel lighter. | More about Buoyancy → |
| Hydrostatic pressure | The squeeze water puts on the body when you are in it. | More about Hydrostatic pressure → |
| Thermoregulation | How the body keeps its temperature steady in heat and cold. | More about Thermoregulation → |
| Immersion | Having the body, or part of it, in water. | More about Immersion → |
Claim and Product Terms
Colon hydrotherapy (also called colonic irrigation or colonics) means cleansing the lower bowel with water. NCCIH describes limited clinical evidence validating it and insufficient evidence for its prescribed uses. [9] The claim check is at colon hydrotherapy.Detox foot bath means a foot bath marketed as drawing out toxins. See detox foot baths and ionic foot spas.
Cold plunge, ice bath, sauna and infrared sauna are covered in depth by the Specialty Topics section: see cold-water immersion and sauna evidence.
Frequently asked questions
Is hydrotherapy the same as balneotherapy?
Not always. One international proposal uses hydrotherapy for plain tap water and balneotherapy for natural mineral waters, gases and peloids. [1] Many sources use the words more loosely.
What is a sitz bath?
It is a shallow bath for sitting in. For one use, the NHS lists taking a warm bath among ways to ease itching and pain from piles. [10] See the sitz bath guide.
What is a scald?
The NHS says scalds are caused by hot liquids or steam. [2]
Does hypothermia only happen in winter?
No. The NHS lists falling into cold water among the causes. [6]
Where can I find a term that is not here?
Use the index of water practices or the category hub.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Safety Terms
| Term | Plain meaning | Read more |
|---|---|---|
| Scald | An injury from hot liquid or steam. [2] | More about Scald → |
| Heatstroke | The NHS calls it a medical emergency. [3] | More about Heatstroke → |
| Fainting | A brief loss of consciousness; the NHS lists being too hot among the causes. [4] | More about Fainting → |
| Low blood pressure | The NHS defines it as a reading of less than 90/60mmHg. [5] | More about Low blood pressure → |
| Hypothermia | A dangerous drop in body temperature below 35C. [6] | More about Hypothermia → |
| Cold shock | The body's sudden reaction to cold water. | More about Cold shock → |
| Afterdrop | A further fall in body temperature after leaving cold water. | Same page as cold shock, above |
| Drowning | The process of experiencing respiratory impairment from submersion or immersion in liquid. [7] | More about Drowning → |
| Legionnaires' disease | A lung infection you can get from breathing in water droplets, including from hot tubs. [8] | More about Legionnaires' disease → |
| Hot tub rash | A rash associated with hot tub use; the linked page covers causes and cautions. | More about Hot tub rash → |
Safety First
References
- Gutenbrunner C, Bender T, et al. 2010. A proposal for a worldwide definition of health resort medicine, balneology, medical hydrology and climatology. International Journal of Biometeorology. Read 2026-10-22.
- NHS. Burns and scalds. Read 2026-10-22.
- NHS. Heat exhaustion and heatstroke. Read 2026-10-22.
- NHS. Fainting. Read 2026-10-22.
- NHS. Low blood pressure (hypotension). Read 2026-10-22.
- NHS. Hypothermia. Read 2026-10-22.
- World Health Organization. Drowning. Fact sheet, 1 May 2026. Read 2026-10-22.
- NHS. Legionnaires' disease. Read 2026-10-22.
- NCCIH. “Detoxes” and “Cleanses”: What You Need To Know. Read 2026-10-22.
- NHS. Piles (haemorrhoids). Read 2026-10-22.