well water vs ground water

well water and ground water both are nouns.

Word	Noun	Adjective	Verb	Adverb
well water	Yes	No	No	No
ground water	Yes	No	No	No

As nouns, well water and ground water are synonyms defined as:

well water and ground water: underground water that is held in the soil and in pervious rocks

Other synonyms of well water include spring water.

well water (noun)	ground water (noun)
underground water that is held in the soil and in pervious rocks	underground water that is held in the soil and in pervious rocks