These exercises can be done in public pools, but there are precautions to be observed. There is little point attempting exercises in the midst of an amateur water polo game, for example. The pool also needs to be accessible for the elderly, or those with disabilities. A strange quirk of working out in water is the 'diving reflex'. With this, the heart actually increases in size by a small amount and is therefore able to pump more blood with each beat, decreasing blood pressure with a lowered pulse rate. The lungs also benefit from the aerobic effect.

 Aquarobic classes can suit almost any level of fitness, from vigorous sessions in cooler pools to a more gentle version in warmer water.

Workouts in spas are possible - and very pleasurable indeed. It seems that a good soaking in the higher temperature of a spa lowers the internal body temperature ('core temperature'), promoting better sleep. This is a great stress reliever

source: bbc.co.uk