water filter vs filter

water filter and filter both are nouns.

Word	Noun	Adjective	Verb	Adverb
water filter	Yes	No	No	No
filter	Yes	No	Yes	No

As nouns, filter is a hypernym of water filter; that is, filter is a word with a broader meaning than water filter:

water filter (noun)	filter (noun)
a filter to remove impurities from the water supply	device that removes something from whatever passes through it
	an electrical device that alters the frequency spectrum of signals passing through it

water filter (verb)	filter (verb)
	remove by passing through a filter
	pass through
	run or flow slowly, as in drops or in an unsteady stream