The term "hydrotherapy" refers to any therapy program that uses water on the outside of the body (as opposed to inside of the body—for example, drinking water). Hydrotherapy can take many forms, such as:

Sitting in a hot whirlpool to warm up joints
Prescribed, supervised physical therapy that takes place in a pool
Doing water aerobics or swimming laps to build strength

Hydrotherapy is not limited to people with arthritis or joint injuries. For example, many serious athletes use ice baths to recover from workouts.

Advantages of Hydrotherapy

Many of the advantages of hydrotherapy are due to hydrostatic pressure—water pressing against a submerged body from all sides. Water even exerts force upwards, against gravity, which is why the body feels lighter in water (buoyancy) and may be able to float.

Hydrostatic pressure:

Takes stress off weight-bearing joints. Buoyancy in water results in less pressure on joints.
Improves blood circulation. Water’s hydrostatic pressure acts as a compression stocking, improving blood circulation.
Increases heart function. Improved blood circulation helps the heart work more efficiently, pumping more blood at fewer beats per minute. (An individual’s target heart rate is typically lower in water than on land.)
Provides added resistance, which can help build muscle. Even simple movements, such as walking, are more challenging when in waist- or chest-deep water.

In addition to the physical benefits caused by hydrostatic pressure, exercising in water seems to improve mood and emotional well-being. Small research studies suggest that regularly exercising in water may help reduce symptoms of depression and anxiety ¹ Silva LAD, Tortelli L, Motta J, et al. Effects of aquatic exercise on mental health, functional autonomy and oxidative stress in depressed elderly individuals: A randomized clinical trial. Clinics (Sao Paulo). 2019;74:e322. PMID: 31271585 doi:10.6061/clinics/2019/e322 ^, ² Kim S, Hsu FC, Groban L, Williamson J, Messier S. A pilot study of aquatic prehabilitation in adults with knee osteoarthritis undergoing total knee arthroplasty - short term outcome. BMC Musculoskelet Disord. 2021;22(1):388. Published 2021 Apr 26. PMID: 33902505 doi:10.1186/s12891-021-04253-1 ^, ³ Silva LAD, Menguer LDS, Doyenart R, et al. Effect of aquatic exercise on mental health, functional autonomy, and oxidative damages in diabetes elderly individuals [published online ahead of print, 2021 Jun 21]. Int J Environ Health Res. 2021;1-14. PMID: 34152875 doi:10.1080/09603123.2021.1943324 and even encourage better sleep. ⁴ Chen LJ, Fox KR, Ku PW, Chang YW. Effects of Aquatic Exercise on Sleep in Older Adults with Mild Sleep Impairment: a Randomized Controlled Trial. Int J Behav Med. 2016;23(4):501-506. doi: 10.1007/s12529-015-9492-0 ^, ⁵ So BCL, Kwok SC, Lee PH. Effect of Aquatic Exercise on Sleep Efficiency of Adults With Chronic Musculoskeletal Pain [published online ahead of print, 2021 Jun 30]. J Phys Act Health. 2021;1-9. DOI: 10.1123/jpah.2020-0476

Warmer water may feel better on stiff joints

While water temperature is a matter of personal preference, warmer water is considered better for loosening stiff joints. Pools specifically designated for therapeutic exercise may be kept at higher temperatures than pools primarily used for lap swimming.

See When and Why to Apply Heat to an Arthritic Joint

Swimming ability is not required

Aquatic exercise can be done in waist- or chest-deep water, so swimming skills are not necessarily required. Regardless of swim abilities, an instructor or lifeguard should always be present.

See Water Therapy for Osteoarthritis

Whirlpool Therapy, Hydromassage, and Balneotherapy

Not all forms of hydrotherapy require physical activity. Passive forms of hydrotherapy may reduce pain and loosen stiff joints. They may also be relaxing and improve mood. A few examples include:

Sitting in a hot water whirlpool for 5 to 20 minutes warms up stiff joints. It may also be relaxing and improve mood.
Hydromassage, or water massage, typically involves sitting or lying down in a water-jet tub. The water jets can be aimed to apply pressure to stiff and painful areas.
Balneotherapy is slightly different than hydrotherapy because it uses mineral waters and muds rather than tap water. While proponents believe the minerals provide added benefits, the science is uncertain. ⁶ Cozzi F, Ciprian L, Carrara M, et al. Balneotherapy in chronic inflammatory rheumatic diseases-a narrative review. Int J Biometeorol. 2018;62(12):2065-2071. doi:10.1007/s00484-018-1618-z ^, ⁷ Santos I, Cantista P, Vasconcelos C. Balneotherapy in rheumatoid arthritis-a systematic review. Int J Biometeorol. 2016;60(8):1287-1301. doi:10.1007/s00484-015-1108-5 ^, ⁸ Verhagen AP, Bierma-Zeinstra SM, Boers M, et al. Balneotherapy (or spa therapy) for rheumatoid arthritis. Cochrane Database Syst Rev. 2015;2015(4):CD000518. Published 2015 Apr 11. PMID: 25862243 doi:10.1002/14651858.CD000518.pub2 This type of therapy is typically offered at facilities advertised as medical spas.

People with weakened immune systems are advised to ask about facilities’ cleaning and maintenance routines. ⁹ Hlavsa MC, Aluko SK, Miller AD, et al. Outbreaks Associated with Treated Recreational Water - United States, 2015-2019. MMWR Morb Mortal Wkly Rep. 2021;70(20):733-738. Published 2021 May 21. PMID: 34014907 doi:10.15585/mmwr.mm7020a1

Ultimately, individuals must decide what works best for their bodies and health circumstances. For example, spending time in a hot whirlpool is discouraged if joints are inflamed.

While considered safe, there is not a lot of research for or against passive forms of hydrotherapy. In contrast, active forms of hydrotherapy have established benefits.

Dr. Catherine Lutsey is a Doctor of Physical Therapy at the Shirley Ryan AbilityLab. She has practiced as a physical therapist for more than a decade, and her specialties include the spine, sports injuries, and arthritis.