Answer:

Use shampoo and conditioner or conditioning shampoo before entering the swimming pool or hot tub. This will provide added moisture and prevent excessive loss of moisture due to chlorine or other chemicals. After swimming, use a clarifying shampoo which will strip damaging chemicals from the hair. For example, Triswim has a line of such products (shampoo, conditioner, body wash, etc.) designed to help serious swimmers overcome the effects of regular swimming. I am sure there are other similar brands as well, this is just one example. These products should also have little affect on properly maintained water in pools or hot tubs. You may have to clean the filter a little more regularly.