Bertie Editorial · Updated 28 July 2026
Walk into two different hydrotherapy centres and you might find two completely different machines: a warm swimming pool at one, and at the other a glass-sided treadmill that fills with water. Both are hydrotherapy. They are not interchangeable, and knowing the difference means you can follow the conversation when a therapist recommends one.
What the pool does
Pool hydrotherapy is supported swimming. Your dog wears a buoyancy vest, the therapist is in the water or at the edge, and the dog swims in short, controlled bursts with rest in between. Because the water carries all of the dog’s weight, joints take no impact at all while the muscles work hard.
That makes the pool the tool for fitness and conditioning, weight loss in dogs who can’t manage long walks, and dogs who can’t bear weight on a limb at all yet. It’s also the option for dogs who simply love to swim and need safe exercise that doesn’t pound their joints.
What the pool doesn’t do is teach a dog to walk correctly. Swimming is a different movement from walking, which is exactly why the second machine exists.
What the treadmill does
The underwater treadmill is a treadmill inside a sealed tank. The dog walks in, the door closes, warm water rises to a height the therapist chooses, and the belt starts moving. The dog walks against the water’s resistance while the water supports part of its weight.
The depth is the clever bit. Water at hip height carries a large share of the dog’s weight; shallower water carries less. As recovery progresses, the therapist drops the water level and the dog gradually takes more of its own weight back, in the same walking pattern it uses on land.
That makes the treadmill the tool for gait retraining after surgery, where the goal is not fitness but teaching the dog to use the repaired leg properly again. It’s the usual recommendation after cruciate ligament surgery rehab referrals, and it suits arthritic dogs who need controlled, even exercise more than they need a swim. It’s also often the gentler introduction for dogs nervous of water, because the water rises slowly around them rather than being something they’re lowered into.
Which one does your dog need?
This is a clinical decision, and the honest answer is that you shouldn’t be the one making it. The assessment at a good centre exists precisely to match the kit to the condition. As a rough map of how therapists tend to think:
| Situation | Usual starting point |
|---|---|
| Post-surgery gait retraining | Treadmill |
| Can’t bear weight on a limb yet | Pool |
| Arthritis management | Either, often treadmill |
| Weight loss and fitness | Pool |
| Nervous of water | Often treadmill first |
Don’t rule out a centre because it only has one machine. If your dog’s condition needs the other kind, a good therapist says so at the assessment and points you to a centre that has it. A centre that insists its one machine suits every dog is showing you a red flag; there’s more on those in choosing a hydrotherapist.
Cost-wise the difference is small, with treadmill sessions usually costing a few pounds more than pool sessions. The cost guide has the full numbers.
Whichever your dog ends up in, the first visit follows the same shape: assessment first, water second. What to expect walks through it.
Your questions, answered
- Is the underwater treadmill better than the pool?
- Neither is better; they do different jobs. The treadmill suits gait retraining after surgery because the dog walks in a controlled pattern against resistance. The pool suits fitness, weight loss and dogs who cannot bear weight at all. The right choice depends on the condition, which is what the assessment is for.
- Why does the treadmill cost more per session?
- The kit is expensive to buy and maintain, and treadmill sessions are usually more hands-on for the therapist, who is often adjusting speed and water depth continuously. The difference is typically a few pounds a session.
- Can a dog use both pool and treadmill?
- Yes, and in longer rehab plans it is common: treadmill work to rebuild a correct walking pattern, pool work for fitness once the gait is sound. The therapist sequences it based on progress.