head gate vs water gate

head gate and water gate both are nouns.

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

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

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

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

head gate (noun)	water gate (noun)
a gate upstream from a lock or canal that is used to control the flow of water at the upper end	regulator consisting of a valve or gate that controls the rate of water flow through a sluice
regulator consisting of a valve or gate that controls the rate of water flow through a sluice