It depends on where you are in your treatment. If you are neutropenic, the answer is no. If you are immune compromised, it's probably a very bad idea. And if you're healthier, proceed with caution. Public swimming pools, and especially hot tubs, can be breeding grounds for germs. Talk to your doctor but perhaps enjoying rays and vitamin D (with proper sunscreen, sunglasses, and head protection) is your better choice. Private pools and hot tubs, if they aren't too crowded with many young children and babies using them, might be just fine.