Many pet reptiles will get enough exercise in their cages but large snakes and large lizards may benefit from swimming. Some lizards enjoy being leash-walked for exercise and some turtles and tortoises benefit from being placed in a large outdoor pen for exercise. It's best to not swim your reptile in the family bathtub. If you must, make sure you thoroughly disinfect it prior to allowing human family members to bathe (one cup of bleach per gallon of water works well).
For more information, please read the story Reptiles Need Exercise, Too