Very thin, brown hair. To lack of hair.

Due to prolonged stress nd over exposure to sun, my once thick black hair have become lifelessly brown and very less in no. My scalp shows off from mainly right hemisphere and back of skull. I once had very thick hair in my school and since i startd swimming, they have just went bad. They start looking healthy when i avoid sun for few months completely and have a good diet, but I feel I need something extra which can give me a permanent solution. Also, I have a great hairfall with the water in my hometown which has high chlorine and fluorine content. Lake water supply gave me very good thick hair in just 2weeks lately. Plz give me some topical as well as diet and exercise tips to get back a healthy scalp, whr my scalp skin isn't visible due to lack of hair.