Death due to disease is called death by natural causes. There are four main types of disease: pathogenic disease, deficiency disease, hereditary disease, and physiological disease. Diseases can also be classified as communicable and non-communicable disease.
A watershed is the area of land where all of the water that falls in it and drains off of it goes to a common outlet.
Drainage Basin / Watershed. The precipitation that falls into a valley, and on surrounding interfluves flows downward usually creating a stream or river. The area of land that contributes water to a stream or river is called a watershed, or drainage basin. Small drainage basins generally contribute to streams, while the water from larger drainage basins come together to form large rivers.