What Is Hydrotherapy? Wellness Use vs Clinical Rehabilitation, Temperature and Evidence

What Is Hydrotherapy

Hydrotherapy is a broad name for using water, at different temperatures, for comfort, relaxation, exercise or rehabilitation. It covers warm baths, exercise in a pool, hot tub and spa use, cold showers and swims, alternating warm and cold water, and sitz baths (sitting in a shallow bath of water). Saunas and steam rooms heat the air rather than immerse you in water, so this library treats them as close relatives and links to the pages that cover them in depth.

The word is used in more than one way. One international proposal reserves "hydrotherapy" for therapy with plain tap water, and uses "balneotherapy" for natural mineral waters, gases and peloids (a word for medical muds, explained on the terms page). [1] In rehabilitation research, "hydrotherapy" is often used for exercise in water, as in a 2026 review of recovery after knee replacement. [2] The page on how the terms differ sorts this out.

Wellness Use and Clinical Rehabilitation

Clinical rehabilitation is water-based exercise or therapy aimed at a health problem, such as knee or hip osteoarthritis or recovery after joint surgery. A Cochrane review of 13 trials found that aquatic exercise caused a small short-term improvement in pain compared with no intervention in people with knee or hip osteoarthritis. [3] After knee replacement, a 2026 meta-analysis found hydrotherapy did not reduce pain more than land-based exercise or usual care, but it did give greater gains in muscle strength. [2]

Wellness use is self-directed: a long warm bath, a spa visit, a cold shower. These practices have their own comfort and safety questions, and the research on them is thinner. The page on wellness hydrotherapy and clinical aquatic rehabilitation explains the difference in aims and claims.

How Water Affects the Body, in Brief

Three things change when you are in water: it holds you up (buoyancy), it presses on the body (hydrostatic pressure), and it is warmer or cooler than the air around you. Reviews of immersion physiology describe a shift of blood toward the chest and a rise in heart output when the body is immersed up to the neck. [4] The NHS notes that, in pregnancy, water can relieve pressure on muscles and joints. [5] Details are in how water affects the body and thermoregulation basics.

What the Evidence Shows

Evidence is uneven across the field. Labels follow the site-wide scale.

Most water trials cannot hide the water from the person in it, so expectation and the pleasure of the experience can influence results. That is a limit of the research, not a reason to dismiss it. See how hydrotherapy is studied and evidence by goal.

Find Your Way Around the Library

• Start here: your first aquatic therapy or spa session, the glossary and frequently asked questions.
• Warm water and aquatic therapy: warm-water bathing and aquatic therapy, warm baths, sitz baths, aquatic physical therapy.
• Cold and heat: cold-water immersion and contrast practices, saunas and steam rooms, and, on the biohacking side, cold and heat exposure.
• Traditions: hot springs and thermal baths, Japanese onsen, balneotherapy in Europe, hammam and Roman baths.
• Evidence by goal: stress, sleep, arthritis, skin.
• Safety: burns and scalds, drowning risk, Legionella, alcohol and drugs.
• People and settings: older adults, infants, accessible bathing.
• Claims checked: red flags in marketing, claims with no good trial support, and common myths.