water wagon vs waggon

water wagon and waggon both are nouns.

Word	Noun	Adjective	Verb	Adverb
water wagon	Yes	No	No	No
waggon	Yes	No	No	No

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

water wagon: a wagon that carries water (as for troops or work gangs or to sprinkle down dusty dirt roads in the summertime)
waggon: any of various kinds of wheeled vehicles drawn by an animal or a tractor

Other hypernyms of water wagon include wagon.

water wagon (noun)	waggon (noun)
a wagon that carries water (as for troops or work gangs or to sprinkle down dusty dirt roads in the summertime)	any of various kinds of wheeled vehicles drawn by an animal or a tractor
	a car that has a long body and rear door with space behind rear seat