It means "by any method available". In this case, probably through streams, rivers and even evaporation.

This literally means "by any way possible." In this context, "means" are the method, or way in which something is done. Usually, I think it is more common to hear this said as "By any means necessary," which implies that there is some ultimate goal and you will do anything you possibly can to get to that goal. Basically, there is nothing you wouldn't do to achieve your goal.

it means that we don't know the way how something occurs but it occurs anyway