water absorption vs absorbency

water absorption and absorbency both are nouns.

Word	Noun	Adjective	Verb	Adverb
water absorption	Yes	No	No	No
absorbency	Yes	No	No	No

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

water absorption: The amount of water absorbed by a composite material when immersed in water for a stipulated period of time.
absorbency: the property of being absorbent

water absorption (noun)	absorbency (noun)
The amount of water absorbed by a composite material when immersed in water for a stipulated period of time.	the property of being absorbent