• 09.018 from the hillside there was a water-gate.
• 09.018 in by the water-gate.
• 09.020 opened the water-gate,
• 09.021 and thought about this water-gate,
• 09.052 which pulled up the portcullis at the water-gate
• 09.056 He heard the creak of the water-gate being hauled up,

Hyphenated in the OED examples.

“water gate, n.2.” OED Online, Oxford University Press, June 2017, http://www.oed.com/view/Entry/226193. Accessed 21 September 2017.