The principle sources of the calcium found in the water of the tertiary Amazonian region near Manaus, are the water running over the tree trunks and the total forest water. The soluble calcium content must come from the rain washing the tree crowns, stems, and leaves, and to a certain point from the dissolution of metabolic products of macro and micro-organisms. Generally, only traces of calcium are found in rain water, soil, and river water. Therefore, calcium can be considered as an element circulating in a closed system. Altogether the calcium content in the natural water of the tertiary Amazon region is extremely low.