Why does rainwater make my hair curly?

Question

and can I use something that works just as well if its not raining?

Answer 1

Is it only rain water or water? If it just rain water then it might to do with the acidic nature of rain water. Rain water is slightly acidic so it may be the reason for curly hair. If you try few drops of citric acid (orange or lemon juice) in water it may work if it has to do with acidic water. If not, it must be something else.