water gate vs penstock

water gate and penstock both are nouns.

Word	Noun	Adjective	Verb	Adverb
water gate	Yes	No	No	No
penstock	Yes	No	No	No

As nouns, water gate and penstock are synonyms defined as:

water gate and penstock: regulator consisting of a valve or gate that controls the rate of water flow through a sluice

Other synonyms of water gate include floodgate, head gate, sluice valve, sluicegate.

water gate (noun)	penstock (noun)
regulator consisting of a valve or gate that controls the rate of water flow through a sluice	conduit that carries a rapid flow of water controlled by a sluicegate
	regulator consisting of a valve or gate that controls the rate of water flow through a sluice