According to The Times (p.12, 13 July 2016)

"Drinking a large glass of water with a meal tricks the brain into thinking you are full, researchers say."

The article does go on to elaborate what the 19 people in the study consumed: 50 ml or water, or 350 ml. Those that drank the greater amount felt fuller.

I don't have any difficulty in believing the findings, even though it was not a proper double-blind trial. (The subjects at least must have an idea how much they drank, even if the researchers didn't.) My own self-experiments, using beer rather than water, strongly confirm the results of the study and suggest it is a repeatable effect, although lacking the surprise factor somewhat.