I know what I want to do but which major is best?

I am interested in water quality but not necessarily becoming a waste water treatment operator. If I did work in a waste water treatment facility I would like to be doing something in a higher capacity if possible. I would ideally like to design water purification systems or build them in countries without access to clean water. I am not sure which degree is best for this goal as there are so many, hydrology, chemical/civil/environmental engineering, biology, various chemistry programs... Any insight provided would be appreciated.