The term 'MAJOR WATER LINE' is composed of two words, the first being 'MAIN' with four letters. MAIN is a noun that refers to the most important or principal part of something, such as a road, river, or pipe. The second word is 'WATER LINE, ' which is a noun that refers to a pipe or conduit that carries WATER from one place to another. Together, the two words form a phrase that describes a large pipe or conduit that carries WATER from one place to another, typically for the purpose of supplying WATER to a large area.