For thousands of years, communities have relied on the natural rolling action of rivers and streams to treat wastes as they moved downstream. As top water cascaded to the bottom and the bottom water rose to the top, oxygen was added by photosynthesis and surface absorption to the entire water column. Suspended solids and wastes settled out to the bottom where they were stored and converted into minerals, gases, and inert ash.
Natural plant and animal life thriving in the highly aerobic environment speeded these treatment processes. Treatment was accomplished so effectively by nature that clean water was available for the next community downstream.