seltzer vs soda water

seltzer and soda water both are nouns.

Word	Noun	Adjective	Verb	Adverb
seltzer	Yes	No	No	No
soda water	Yes	No	No	No

As nouns, seltzer and soda water are synonyms defined as:

seltzer and soda water: effervescent beverage artificially charged with carbon dioxide

Other synonyms of seltzer include carbonated water, club soda, sparkling water.

seltzer (noun)	soda water (noun)
naturally effervescent mineral water	effervescent beverage artificially charged with carbon dioxide
effervescent beverage artificially charged with carbon dioxide	a sweet drink containing carbonated water and flavoring