Exercising in water makes you feel about 90 percent lighter. When you jump or run in the water, your body does not experience the same impact that those moves cause when done on land. This makes it an ideal activity for those with arthritis, back problems, foot or leg injuries, and knee conditions. You can expect to burn between 400 and 500 calories per hour in a water aerobics class (the actual amount will depend on several criteria). By exercising in water you work against 12 times the resistance of air. This helps to develop muscle - which translates to a higher metabolism and healthier body. Of course, another plus, besides being fun, the water helps cover your movements so you don’t need to be self-conscious while exercising.