Hydrotherapy for Injury Recovery: When to Start & What It Does

Key Takeaways

Hydrotherapy lets you start moving sooner after an injury because water supports your body weight and reduces joint stress. At chest depth, you carry only 25–35% of your normal weight.
A study of 287 patients who entered the water within 4–14 days of surgery found no increase in wound-related complications — and noted better pain reduction, less swelling, more strength, and improved range of motion compared to waiting longer.
A randomised trial of elite athletes with severe ankle sprains found aquatic therapy started within 1–7 days of injury was effective for rehabilitation alongside conventional physiotherapy.
Most people can start hydrotherapy 2–6 weeks after surgery, depending on wound healing. Arthroscopic procedures heal faster (around 2 weeks); joint replacements need 4–6 weeks.
Hydrotherapy does not replace land-based rehabilitation. It complements it — particularly in the early stages when land exercise is too painful or risky.

Why Water Helps Injuries Heal Faster

When you are injured, you face a frustrating problem: your body needs movement to heal, but movement hurts. Muscles waste within days of inactivity. Joints stiffen. Cardiovascular fitness drops. The longer you stay still, the harder it is to get back to normal.

Water solves this by changing the rules. Three properties of water make movement easier and less painful:

Buoyancy takes weight off your injury. At chest depth, water supports 60–75% of your body weight (Harrison et al., 1992). An 80 kg person effectively weighs 20–30 kg. This means you can walk, bend, and exercise with far less force going through your injured joint, bone, or muscle.
Warmth reduces pain and muscle spasm. Warm water (33–36°C) activates nerve receptors that compete with pain signals, turning down the pain volume. It also relaxes tight muscles around the injury site, which often cause more pain than the injury itself.
Hydrostatic pressure controls swelling. Water pushes evenly on all submerged tissue, compressing excess fluid out of swollen areas and back into circulation. This is similar to wearing a compression bandage — but applied to your entire body.

The result: you can exercise earlier, with less pain, and with less swelling than you could on land. And earlier exercise leads to faster recovery.

How Soon After an Injury Can You Start?

This depends on the type of injury and whether there is an open wound.

Sprains and strains (no open wound)

You can often begin gentle water-based movement within a few days. A randomised trial with elite athletes who had grade III ankle sprains (the most severe, involving a complete ligament tear) started aquatic rehabilitation within 1–7 days of injury. The aquatic therapy group showed effective recovery in pain, swelling, range of motion, and function.

For less severe sprains, gentle pool walking or range-of-motion exercises in warm water can usually begin after 48–72 hours, once acute swelling has peaked.

After surgery

The key factor is wound healing. You cannot enter a pool with an open or draining wound because of infection risk. General guidelines:

Arthroscopic surgery (small incisions): typically safe to enter water after about 2 weeks, once sutures or staples are removed and the wound is sealed.
Total knee or hip replacement (larger incisions): usually 4–6 weeks, depending on wound healing.
ACL reconstruction: typically 2–4 weeks, though some programmes use waterproof wound coverings to start earlier.

A study of 287 adult patients placed into aquatic environments within 4–14 days after surgery found that early water exposure did not increase wound-related complications. The early aquatic group showed better pain reduction, decreased swelling, increased strength, and improved range of motion.

Important: Always get clearance from your surgeon or physiotherapist before entering a pool after surgery. These timelines are general — your specific wound, procedure, and healing rate determine the right time for you.

Fractures

After a fracture, you typically need to wait until the cast or brace is removed and your consultant confirms the bone is stable enough for aquatic exercise. This is usually 4–8 weeks for most fractures, though it varies widely depending on which bone, how severe the break, and whether surgery was needed.

Once cleared, pool-based exercise is particularly valuable for fracture recovery because the buoyancy lets you load the bone gradually. Bones need some stress to heal properly (this stimulates new bone formation), but too much stress too soon risks re-injury. Water gives you a controlled middle ground.

Hydrotherapy by Injury Type

Knee injuries (ACL, meniscus, patella)

Knee injuries are the most common reason for hydrotherapy referral. The knee bears significant load during walking, and reducing that load in water allows earlier rehabilitation.

A clinical commentary on aquatic therapy after ACL reconstruction noted that underwater treadmill training produced greater gains in knee flexion and muscle size than stationary cycling — suggesting water-based walking may better prevent the muscle wasting that commonly follows knee surgery.

Typical pool exercises for knee injuries include: walking in water, step-ups on a submerged step, leg extensions against water resistance, squats in chest-deep water, and cycling movements while holding the pool edge.

Back injuries

Back pain is the condition with the strongest evidence for aquatic therapy. A 2022 JAMA Network Open trial found that aquatic exercise was more effective than standard physiotherapy for chronic low back pain, with 54% of aquatic patients achieving clinically meaningful pain improvement at 12 months vs. 21% in the physiotherapy group (Peng et al., 2022).

For acute back injuries (disc herniations, muscle strains), water is valuable because spinal loading drops dramatically when submerged. Pool walking, gentle twisting movements, and supported floating all allow spinal movement without the compression that makes land-based exercise painful.

Shoulder injuries

Shoulder rehabilitation in water benefits from a different property: water resistance is proportional to speed. Move your arm slowly through water and the resistance is gentle. Move it faster and resistance increases. This lets you control the intensity of shoulder exercises precisely — something that is harder with weights or resistance bands on land.

For rotator cuff injuries, frozen shoulder, or post-surgical shoulder rehab, pool-based exercises allow early range-of-motion work in a supported environment.

Ankle and foot injuries

The ankle sprain trial mentioned above showed aquatic therapy can begin very early — even within the first week for severe sprains. Walking in water allows you to practice a normal gait pattern while bearing only a fraction of your body weight, which is critical for retraining balance and coordination after ankle injuries.

What a Recovery Session Looks Like

A typical physiotherapist-led hydrotherapy session for injury recovery follows this structure:

Warm-up (5 minutes): Gentle walking in the pool, arm movements, acclimatising to the temperature.
Targeted exercises (20–30 minutes): Your physiotherapist guides you through exercises specific to your injury. These might include walking patterns, resistance movements, stretches, balance challenges, or specific joint exercises. Intensity increases gradually over weeks.
Cool-down (5 minutes): Slow walking, gentle floating, or stretching.

Sessions usually run 2–3 times per week for 6–12 weeks. Most research showing lasting benefits used this frequency.

When Hydrotherapy Is Not the Right Choice

Open or draining wounds. Infection risk is too high. Wait until the wound is fully sealed.
Active infections. Do not enter a pool if you have a skin infection, chest infection, or urinary tract infection.
Unstable fractures. If the bone is not yet stable enough for movement, water exercise is premature. Follow your consultant’s guidance.
Severe cardiovascular conditions. The combination of warm water and hydrostatic pressure increases cardiac workload. Get medical clearance first.
Late-stage rehabilitation. Hydrotherapy is most valuable in the early and mid stages of recovery. As you get stronger, you need to transition to land-based exercise to rebuild the strength, balance, and impact tolerance you need for daily life.

The Bottom Line

Hydrotherapy helps injuries heal faster for a simple reason: it lets you exercise sooner and with less pain. The water takes weight off your injury, reduces swelling, and dulls pain — creating a window where movement is possible when it otherwise would not be.

The evidence supports this across injury types: ankle sprains, knee surgery, back pain, and fractures all show faster recovery timelines with aquatic therapy. It is not a replacement for surgery, medication, or land-based physiotherapy. It is a bridge — getting you moving in the critical early weeks when inactivity does the most damage.

Ask your surgeon or physiotherapist about hydrotherapy. The sooner you start, the sooner you recover. Our equipment guide covers home options for ongoing recovery.

References

Peng, M-S. et al. (2022). Efficacy of therapeutic aquatic exercise vs physical therapy modalities for patients with chronic low back pain. JAMA Network Open, 5(1), e2142069. PMC8742191
El-Shamy, F. et al. (2024). Effect of aquatic versus conventional physical therapy program on ankle sprain grade III in elite athletes: randomized controlled trial. Scientific Reports. PMC11238378
Mooventhan, A. & Nivethitha, L. (2014). Scientific evidence-based effects of hydrotherapy on various systems of the body. North American Journal of Medical Sciences, 6(5), 199–209. PMC4049052
Harrison, R.A., Hillman, M. & Bulstrode, S. (1992). Loading of the lower limb when walking partially immersed. Physiotherapy, 78(3), 164–166.
Villalta, E.M. & Peiris, C.L. (2013). Early aquatic physical therapy improves function and does not increase risk of wound-related adverse events for adults after orthopedic surgery. Archives of Physical Medicine and Rehabilitation.

Last reviewed: February 2026. This article is for informational purposes and does not replace medical advice. Always get clearance from your surgeon or physiotherapist before starting hydrotherapy after an injury.

Hydrotherapy for Injury Recovery: When to Start, What It Does, and What the Evidence Shows

Why Water Helps Injuries Heal Faster