drain system vs stormwater drain

drain system and stormwater drain both are nouns.

Word	Noun	Adjective	Verb	Adverb
drain system	Yes	No	No	No
stormwater drain	Yes	No	No	No

As nouns, drain system and stormwater drain are synonyms defined as:

drain system and stormwater drain: a system of watercourses or drains for carrying off excess water

Other synonyms of drain system include drainage well, storm drain, storm sewer.

drain system (noun)	stormwater drain (noun)
a system of watercourses or drains for carrying off excess water	a system of watercourses or drains for carrying off excess water