The relationship between human beings and water is like the relationship between humans and life itself.  The movements of nomadic people were guided by the need for water.  Food?  Of course.  But food, especially the buffalo hunters, moved around.  Water was where you found it and when you searched for new food, you encamped where there was water before hunting.  This young lady appeals to the water spirits for good fortune and that there will always be a good source of clear water for her use.  Maybe we should do the same thing because we are running short of clean water.