Written in co-operation with:
Johan Lambeck Bsc., IATF Senior Lecturer
Edited by:
drs. Ing. Eric Legdeur Msc, Owner-Manager EWAC BV


Physical medicine and rehabilitation aims to enhance and restore functional ability, independence and quality of life to those with physical impairments or disabilities, irrespective of age, affecting the brain, spinal cord, nerves, bones, joints, ligaments, muscles, and tendons (source: AAPMR).

It is a multi-disciplinary approach in which also aquatic rehabilitation, mostly by a physiotherapist, is a valuable intervention. A pool is a safe environment in which exercises can be performed with a low mechanical impact, though at the same time a high physiological load. Exercise dosage can be varied easily and equipment supports the clinical decision making about goals, intensity and method.

Hydrotherapy equipment fulfils an important role in water-based rehabilitation.

Create a safe and low impact exercise environment

Hydrotherapy equipment helps physiotherapists and rehabilitation experts to create an aquatic environment that is safe to exercise in. It helps therapists to make the most of the unique properties water has to offer:

  • Reduced gravity
  • Warmth, which reduces muscle tension and increases joint mobility
  • Resistance to movement, slowing down all exercises
  • Increase of the central blood volume, increasing the heart’s efficiency
  • An unbalancing effect, strengthening the core muscles
  • Strong water currents can assist in underwater massage, but also balance and strength training
Therapist and patient in Aquatic Therapy session
Therapist and patient in Aquatic Therapy session

What is aquatic therapy and what is hydrotherapy?

In both cases it is therapy with water (aqua = Latin and hydro = Greek). Let’s start with some history. The use of the beneficial effects of water goes back more than 4000 years and has been recorded in Roman, Greek, and even Egyptian civilizations. it is a known fact that Egyptian royalty bathed in water with essential oils and flowers, while the Romans had public baths for their citizens. Hippocrates, Greek physician and founder of modern medicine thinking, prescribed bathing in spring water for sickness. Other cultures with a very long history in hydrotherapy include Japan and China, where in Japan hydrotherapy was centered around Japanese hot springs or “onsen”. This was even long before the Romans invented their “Thermae” or bathing houses.

The word Hydrotherapy was narrowed down to therapy in water (with complete immersion) in the English Commonwealth and also used in The Netherlands as hydrotherapie. In Germany however, therapy in water is called Wassertherapie, whilst therapy with water such as showers, arm/leg baths and so on are called Hydrotherapie. In the USA, the term hydrotherapy is used similar to Germany and the term Aquatic Therapy is used for therapy in water. During the last decade however, the term Hydrotherapy has gradually been replaced by the term Aquatic Therapy.  For example: the English “Hydrotherapy Association of Chartered Physiotherapists” has been renamed “Aquatic Therapy Association of Chartered Physiotherapists” in 2008. Aquatic therapy can be done by any registered health professional, e.g. aquatic physiotherapy or aquatic occupational therapy. A definition is: Aquatic (Physical) Therapy – APT – is a program, using mechanical and thermal characteristics of water during partial or complete immersion, in combination with the effects of movement. It evokes short-term and long-term adaptational mechanisms of a person with a deranged biological system, using specific stimuli to create biological adaptations and thus therapeutic effects. APT is mostly focused on children and adults with neuromusculoskeletal impairments, as well as supporting systems like the cardiovascular-, pulmonary- or metabolic system.

Low gravity environment and water temperature

The more difficulty a person has on land (mostly with gravity) the more possibilities aquatic therapy offers. In those cases, movement intensity can be very low, or even only passive movements are possible. Water temperature has to be adapted to the thermal comfort of the person and therefore the regular temperature in aquatic therapy pools is around 31 °C ±2 °C. There is a tendency to increase the exercise intensity and therefore temperatures tend to be below 30 °C.

Intensity of the exercises

After an aquatic therapy session, a client should be tired in order to evoke adaptational processes in tissues and systems. Research has shown that water is an ideal medium for this. This should lead to functional gains on land in order to increase participation (again). This gives the difference between aquatic therapy and swimming: aquatic therapy is physical exercise in a pool, to be used on land. Swimming is physical exercise done in a pool. Swimming can be used therapeutically of course, just like walking or cycling. But aquatic therapy includes more specific methods to gain the desired therapeutic goals. The International Classification of Function, Disability and Health (ICF) is normally used to streamline goal setting. Examples at the level of function and structure are: muscle strengthening, joint mobilization. Examples of goals at the level of activity are: walking stairs, transferring the center of gravity, reaching and grasping. Quality of Life, self-efficacy and resilience are goals that can be added to the ICF’s goals.

Therapist performing relaxation exercises with patient
Therapist performing relaxation exercises with patient

Complementary to regular physiotherapy

Aquatic therapy is mainly based on physiotherapy, and is performed by professional physiotherapists that have received specific post-graduate education. In this way it is prevented that land-based physiotherapy is performed in a pool without using the specific advantages that water has to offer, as mentioned above. Methods can be passive (joint manipulations in water), but most are active. Most aquatic therapy pools can be found in centres for rehabilitation and hospitals, where clients have to relearn lost skills.

Aquatic Therapy can be viewed as a specialized form of physiotherapy, which involves the use of water to reach similar improvement goals such as:

  • bodily balance
  • range of motion of the joints
  • trunk stability and flexibility
  • movement control
  • walking patterns
  • reduced pain sensation

Buoyancy in water reduces gravity

Water, compared to other methods of rehabilitation, offers lots of advantages. Because of buoyancy, less gravity (and thus weight-bearing) is experienced so that persons who have to fight against gravity – e.g. because of muscle weakness – are better able to keep the trunk upright or move limbs. Research shows that trunk muscles need about 25% of the force to stabilize the trunk in comparison to land. This means that less co-contraction is seen in the water, which in its turn allows joints to move more physiologically.

Hydrostatic pressure supports blood circulation, necessary to supply tissues with water, nutrition and oxygen as well as depleting metabolic waste products. This supports muscle function.

Hydrostatic pressure differences are the basis for the resistance of water against movement. The magnitude of this resistance is partly based on the density of the liquid, being much higher in water than in air.

Active hydrotherapy equipment
Body weight reduction as a result of immersion

Would you like to learn more about the basics of hydrotherapy? Request information about the hydrotherapy training we offer.

The difference between passive and active hydrotherapy

In passive hydrotherapy, the individual is passive and immersed in water, receiving treatment by just being immersed (e.g. floating), from a hydrotherapy appliance such as a massage bath, or from a therapist. A therapist can manipulate joints or apply massage techniques in order to influence pain or to increase the range of motion.

Passive practice of hydrotherapy, therapist with individual in water
Passive practice of hydrotherapy, therapist with individual in water

Classic hydrotherapy mostly involves individuals who are stationary in a bath, soaking and relaxing in the warm water. That’s what we call passive stationary exercises and immersion. Around the years 1700 – 1800, several inspired doctors who were not afraid to experiment, started to introduce several treatments involving immersion. These treatments could involve the use of medicinal herbs, underwater massages, and underwater joint manipulation. Others, especially Sebastian Kneipp, introduced the concept of hot/cold treatments to increase the circulation of the body, which offered beneficial effects on the body.

In modern hydrotherapy thinking, we still regard these treatments as passive as the individual receives the treatment, instead of the individual taking a physically active role in their rehabilitation. Still, a person can be actively involved by feeling changes in the body, as during the relaxation method according to Jacobson (proprioceptive discrimination training as also in mindful concepts).

In active aquatic therapy, persons use their motor output system: using muscles to generate a force. This can be at any level of force production: fine tuning of small spinal muscles at 5% of the maximum till over 100% in the eccentric phase of a plyometric contraction. An example of an aquatic “strengthening”  technique is the Bad Ragaz Ring Method. Apart from hands-on, also hands-off methods are used. In the latter case, mostly with aquatic resistance equipment.

Strengthening serves coordination in activities of daily living. This means that  – postural – coordination training is another important part of active aquatic therapy. Mostly this is related to standing and walking (ask patients in a rehab center about their goals and always they will tell: “I want to walk again: safe, alone, fast”. Standing and walking can lead to falling, in order to train to prevent falling, EWAC designed the obstacle course.

Balance training on the obstacle course
Balance training on the obstacle course

The obstacle course is ideal to train unexpected perturbations. When a person reacts too late: stumbling or even falling will be a slow process that still might be corrected. Turbulent water perturbs posture in a very “water specific” way. In order to increase perturbing forces even more, underwater jets can be used.

Counter current
Counter current

Walking mostly is an automatic process: we think of other things while walking. To train this automatism, a person needs to repeat a lot: this is to calibrate the central pattern generators for locomotion and to train muscular – and cardiovascular endurance. For this EWAC offers an underwater treadmill.

Active hydrotherapy, individual on underwater treadmill in pool
Active hydrotherapy, individual on an underwater treadmill in a pool

Of utmost importance is the possibility for a person to move freely in a safe environment, while interacting with others. This opens possibilities to enrich the environment and train executive functions, mostly in serious gaming-like activities. To play = to learn, but also to distract and to relax in order to build resilience and self-efficacy.

Get in touch with our team to receive more information or visit our knowledge base

Do you need practical training? Sign up for the hydrotherapy training we offer.

Active hydrotherapy equipment

The right depth, essential in active hydrotherapy

When should you choose for fixed depth or variable depth? Standard concrete or modular pools have a fixed depth and are suitable to carry out active hydrotherapy. At the same time, no individual is alike. There is a large variability in height, as well as their diagnosis and ability to move. For instance, for children to experience an optimal exercise environment, a different depth is needed than for a basketball player. This is why the movable floor was invented as one of the most important types of hydrotherapy equipment for active hydrotherapy. The movable floor enables the therapist to set a depth according to the needs of the individual, exactly adjusted to the exercises intended.

Movable floor with underwater treadmill
Movable floor with an underwater treadmill (active hydrotherapy equipment)

In a pool with a movable floor, the therapist can easily change the depth to suit the needs of both the therapist and the individual. Furthermore, a movable floor enables the therapist to increase the amount of weight that is carried by the joints and the spine as the individual make progress in their abilities. Furthermore, the movable floor can be set to deck level for easy transfer. Therefore, to create an optimal environment for active hydrotherapy, one cannot cope without this important piece of hydrotherapy equipment.

Take a look at our movable floor

Stainless steel versus concrete pools

A swimming pool is probably the most important tool of active hydrotherapy equipment. Also it is one of the most expensive in terms of investment, maintenance and energy consumption. Therefore choosing the right pool for the application of hydrotherapy is essential in the success of water-based rehabilitation. But what are the differences between concrete and modular pools? For more information about the structural differences between concrete vs stainless steel pools, see our article “Why stainless steel is better than concrete”.

Concrete pool
Example of a concrete pool before fitting the movable floor
Example of a concrete pool before fitting the movable floor

Pools are usually built out of concrete, and covered by a watertight lining and tiles to keep the water in. Modern hydrotherapy pools are usually equipped with a movable floor to be able to change the pool depth. Also, these pools can be equipped with observation windows, to give the therapist a good view of the way in which exercises are carried out. As a more modern option, however, it is also possible to fit a concrete pool with underwater cameras enabling the therapist to have a full view of the exercises and to store images for registering progress.

Many of our clients choose a concrete pool with a movable floor, because concrete is easy to form in any size or shape, available worldwide and relatively low in cost. Another factor is that many locations already have an existing pool where they would like to add a movable floor into.


Stainless steel Modular pool
Al Jalilah Children's Hospital Dubai
Modular pool Al Jalilah Children’s Hospital Dubai, equipped with an underwater treadmill, camera’s lighting and several treatment stations

As an alternative to concrete pools, many rehabilitation centers choose a more flexible and adaptable option which is a modular pool. A modular pool is a piece of hydrotherapy equipment that can be installed in every available room, effectively turning this room into a hydrotherapy area. The modular design includes several panels, that can be bolted together on-site to form the pool. All the elements arrive at the site prefabricated and within 10 days of installation time, one can have a fully functional stainless steel pool with excellent hygienic properties. Just as any concrete pool, a modular pool can be fitted with a movable floor, observation windows, cameras, and underwater treadmills. Contrary to concrete pools however, a modular pool can also be deconstructed and restored elsewhere if necessary.

Our clients mainly choose a modular pool when there is an existing location, but no concrete pool. Another reason is often that modular pools are relatively faster to build and assemble on site. The client has a single point of contact during the construction phase of the pool, after which the pool is virtually maintenance-free, guaranteeing optimal uptime of the facility.

Take a look at our modular pool

The unique added value of an Underwater treadmill

The most advanced accessory on the market now is the underwater treadmill. The underwater treadmill can be integrated into the pool bottom, or even on the movable floor. When the underwater treadmill is integrated into the movable floor, this enables the individual to perform stationary walking exercises under variable gravity conditions, which opens up a very large range of treatment possibilities for the therapist. The underwater treadmill is programmable so that the training regimen can be adapted to the specific needs of the individual. Combined with an underwater camera system for recording session data, the underwater treadmill is one of the most versatile pieces of hydrotherapy equipment.

As stated before, the treadmill enables a person to perform large amounts of repetitions, which fits in the concept of massed practise. Moreover, by varying the speed at random, also gait variability can be trained. As the father of modern motor learning, Nikolai Bernstein stated “repetition without repetition”.

Underwater treadmill in modular poolUnderwater treadmill in a modular pool, Pok Hoi Hospital, Hong Kong

Take a look at our underwater treadmill

Self-propelled underwater treadmill

In some circumstances, investing in an electrically operated underwater treadmill is just not an option. In this case, it is still well possible to perform stationary walking exercises underwater using the Pooltrack® Curve. The Pooltrack® curve is a piece of hydrotherapy equipment enabling individuals to perform a walking kind of motion on a set of underwater rollers. This helps in muscle control and increases trunk stability.

Pooltrack Curve in action under water
The EWAC Medical Pooltrack Curve self propelled underwater treadmill

Take a look at our Pooltrack Curve

Underwater bicycle, a home trainer in water

Another very versatile piece of hydrotherapy equipment is the underwater bicycle. This underwater bicycle works like a water-based home trainer and uses the unique properties of water to create a speed-dependent amount of resistance. If the water depth can be varied using a movable floor, the therapist can offer a large range of treatment conditions to train with the underwater bicycle.

Underwater bicycle in knee deep water
Underwater bicycle in knee deep water

Take a look at our underwater bicycle

Obstacle course, for safe balance control

With an underwater obstacle course, a very challenging underwater obstacle circuit can be created and individuals can be trained in pro-active and reactive balance control abilities. The underwater obstacle course consists of several items, ranging from balance beams, to underwater hurdles, to a wiggle board and a reaching pole to imitate several scenarios that can occur in daily life.

Therapist with individual in pool with obstacle course
A therapist with an individual in the pool with an obstacle course

Take a look at our underwater obstacle course

Passive hydrotherapy equipment

The Hubbard tank or butterfly bath. A butterfly-shaped bath for passive stationary exercises

A special case of a bath designed for passive aquatic therapy is the Hubbard tank or butterfly bath. The butterfly shape of this bath allows individuals the full range of motion of the limbs, while at the same time, the therapist can easily reach the important muscles from all sides, for instance, to help to flex the joints or applying underwater massage.

Butterfly bath - Hubbard Tank equipped with Aqua Control water treatment system
Butterfly bath – Hubbard Tank equipped with Aqua Control water treatment system

Active hydrotherapy equipment usually offers more range of motion than passive hydrotherapy equipment. Instead of a therapist performing the actions on the individuals, however, they carry out their movements themselves. For active hydrotherapy, we advise our clients to choose larger hydrotherapy equipment such as a movable floor in a concrete pool or a modular pool.

Take a look at our butterfly  bath / Hubbard tank

Smaller baths and pools for passive hydrotherapy

Passive hydrotherapy equipment involves smaller baths and pools. As the individual is stationary, the need to accommodate a large range of motion is limited. Some of the passive hydrotherapy baths are comparable in size and shape to a normal bath, which one would use at home. These baths can come equipped with lots of functions to stimulate the body to get the blood flowing, for instance:

  • underwater massage (to be applied by the individual or the therapist)
  • underwater currents (whirl effects)
  • bubbles and vibrations
  • electro-galvanic currents through the water
Four Cell bath for passive hydrotherapy
Four Cell bath for passive hydrotherapy

Take a look at our range of wellness baths

Safety and water hygiene in hydrotherapy

Because of its special nature, care should be taken in selecting the proper kind of hydrotherapy equipment. In most hospitals or rehabilitation centers, there is limited experience available with working with water or pools. Because the pools are used with individuals that are susceptible to infection, special care must be taken for water hygiene. Unless the water is replaced after each session, a hydrotherapy pool needs to have a water treatment plant, to perform at least the following basic functions:

  • disinfection with a disinfecting agent such as chlorine or bromide
  •  filtration, to take solid contaminants out of the water
  • circulation
  • heating, to maintain a proper temperature for hydrotherapy
Water treatment plant for pool
Water treatment plant for pool

Take a look at our water treatment systems

Improving pool accessibility with hoisting equipment

In designing an area for hydrotherapy, one should take into account the patient flow, through changing area with showers and toilets, to the pool and back to the changing area. The pool area needs special provisions such as hoisting equipment and stairs for patients to be able to enter and exit the pool in an easy manner. The transfer accessories can be deployed in the absence of, or complementary to a movable swimming pool floor.

Hoisting chair suspended from overhead lifter
Hoisting chair suspended from overhead lifter

Take a look at our transfer accessories

Increase the possibilities, add a movable floor to your swimming pool

Before designing a hydrotherapy area, however, one should consider the variability of individuals that will make use of the hydrotherapy equipment. Active and passive hydrotherapy requires different sets of equipment, and especially in active hydrotherapy, it is important to consider the option of a movable floor to increase the range of possible exercises and range of individuals that can be treated in the pool.

EWAC Medical can take an active role in designing the hydrotherapy area in any application, based on the requirements of the customer.

Enquire now

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