Now let's add water!
It was much easier to find explanations for treatment of children with special needs while in a pool.
Below is a summary of what I found.
The properties of water, such as hydrostatic pressure, turbulence, viscosity, and temperature all play a role as to why a well-planned treatment in the water is effective.
The deep pressure exerted by the water on the body is present the entire time the child is in the water, thereby providing much needed calming tactile stimulation to the child who is highly sensitive to touch.
Pressure and viscosity also help children with gravitational insecurity to have a better sense of security; any potential “fall” will not hurt as it would if they fell on the pavement.
The resistance water provides makes moving three times more difficult than on land. This provides a lot more input to the “muscle sense” or the proprioceptive system (the unconscious perception of movement and spatial orientation arising from stimuli within the body itself). Children with problems in this sensory aspect are often clumsy, do not know their own strength, play too roughly, engage in a lot of “crashing play”, are very fidgety and hyperactive. On the other end of the continuum of proprioceptive problems, the child may appear limp or lethargic, have poor posture, and have problems with balancing activities.
Engaging in well-directed activities in the water helps the child gauge his own body boundaries better, allows him to regulate the force his body exerts when playing or working on tasks (thereby avoiding hurting himself and others), and improves his posture and coordination.
Last but not least, the amount of energy required to do activities in the water helps decrease the child’s hyperactivity, resulting in a better ability to concentrate on tasks afterward, improve sleep patterns and eating habits.