There is no pure water in nature. Since water is a universal solvent, it contains a large array of inorganic and organic compounds which are present as dissolved solids and gases. Even distilled water usually carries enough trace nutrients to support the growth of bacteria and algae. In fact, if a container of distilled water is placed outdoors, life will quickly colonize it.

The chemical composition of natural waters is controlled by rainfall, erosion and dissolution, evaporation, and sedimentation. Since solutes are washed out of rocks, water chemistry reflects the chemistry of the soil and rocks that runoff and groundwater pass over or through in order to arrive at the lake or stream.