Water therapy is a broad term that covers two distinct practices: using water externally to treat pain, aid recovery, and improve mobility (known as hydrotherapy), and drinking water on a specific schedule for claimed health benefits (sometimes called Japanese water therapy). Both fall under the “water therapy” umbrella, but they work in completely different ways and have very different levels of scientific support.
Hydrotherapy: Water as Physical Treatment
Hydrotherapy uses the physical properties of water, including its temperature, pressure, and buoyancy, to treat symptoms throughout the body. You might also see it called aquatic therapy, pool therapy, or balneotherapy. The most common forms include soaking in hot or cold water baths, applying pressurized water jets to the body, and using temperature-based treatments like ice packs or saunas.
What makes water so useful therapeutically comes down to basic physics. When you’re submerged, the upward force of the water nearly equals your body weight, creating a sensation close to weightlessness. This dramatically reduces the load on your joints, making movement possible for people who find land-based exercise painful. At the same time, submersion shifts about 500 to 700 ml of fluid back into your bloodstream that would otherwise pool in your lower body due to gravity. That fluid redistribution is why spending time in water can reduce swelling in your legs and feet.
Therapeutic pools are typically kept between 87°F and 95°F (30.5°C to 35°C), warm enough to relax muscles and ease stiffness without overheating you during exercise. Water below 70°F (21°C) is classified as cold, because your body loses heat 25 times faster in water than in air.
Aquatic Exercise for Arthritis and Joint Pain
Aquatic exercise has some of the strongest evidence behind it for people with osteoarthritis. A systematic review of 20 studies found that aquatic exercise reduced pain by a meaningful margin compared to doing nothing, and also improved joint function. The buoyancy of the water lets people with knee or hip osteoarthritis do strengthening and stretching exercises they couldn’t tolerate on land. Sessions in the research typically lasted about 50 minutes, three days per week, over several months.
One thing worth knowing: when aquatic exercise was compared head-to-head against land-based exercise in some studies, the pain reduction was similar between the two. The advantage of water isn’t necessarily a bigger improvement. It’s that the water makes exercise accessible for people who would otherwise struggle to exercise at all. If walking on a treadmill is too painful for your knees but walking in chest-deep warm water isn’t, aquatic therapy gets you moving when nothing else can.
Cold Water Immersion for Recovery
Athletes and gym-goers often use cold water immersion (ice baths) to recover from intense workouts. A large network meta-analysis compared different combinations of water temperature and soak duration to find what works best. The results were clear: 10 to 15 minutes of immersion produced the most consistent benefits. Shorter soaks didn’t do as much.
For reducing delayed-onset muscle soreness (the ache you feel a day or two after hard exercise), water between 11°C and 15°C (about 52°F to 59°F) was most effective. For recovering explosive power and clearing muscle damage markers from the blood, slightly colder water between 5°C and 10°C (41°F to 50°F) worked best. In both cases, the sweet spot was a medium-length soak of 10 to 15 minutes. Very short dips or extremely prolonged sessions didn’t outperform this range.
Japanese Water Therapy
Japanese water therapy is a drinking-based practice, not a physical treatment. The protocol involves drinking four to six glasses of room-temperature water (roughly 800 to 1,200 ml) immediately after waking up, on an empty stomach, then waiting 45 minutes before eating breakfast. At each meal, you eat for only 15 minutes and then wait at least two hours before consuming anything else.
Proponents claim this routine improves digestion, boosts energy, and helps with weight loss. Some of these claims have a basic logic to them: drinking water before meals can make you feel fuller and eat less, and many people are mildly dehydrated in the morning. But the specific protocol itself, with its precise glass counts and timing windows, has no clinical trials supporting it as a treatment for any condition. The health benefits attributed to it are largely the benefits of staying well hydrated in general.
For reference, the National Academy of Medicine suggests a general daily fluid intake of about 13 cups (104 ounces) for men and 9 cups (72 ounces) for women. These aren’t strict targets, and individual needs vary with activity level, climate, and body size. Drinking four to six glasses first thing in the morning isn’t harmful for most people, but it can cause discomfort, nausea, or bloating, especially if you’re not used to it.
Safety Considerations
Hydrotherapy is generally safe for healthy people, but certain conditions require caution. Rapid temperature changes, like jumping into cold water after a sauna, can trigger blood vessel spasms that pose risks for anyone with heart disease or coronary risk factors. Cold water immersion can cause temporary heart rhythm irregularities in people with existing cardiac problems. Sudden immersion in ice-cold water has also been linked to transient fluid buildup in the lungs.
Heat-based water therapy, including hot tubs and saunas, is a concern during early pregnancy because elevated body temperature may affect fetal development. People with open wounds, active infections, or uncontrolled blood pressure should also approach hydrotherapy cautiously. If you’re using aquatic therapy for rehabilitation, working with a physical therapist who can adjust water temperature, depth, and exercise intensity to your condition makes a significant difference in both safety and results.