well water vs spring water

well water and spring water both are nouns.

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

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

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

Other synonyms of well water include ground water.

well water (noun)	spring water (noun)
underground water that is held in the soil and in pervious rocks	water from a spring
	underground water that is held in the soil and in pervious rocks