From the BBC:
"A previous study found that middle-aged and older people who drank two glasses of water before eating a meal ate between 75 and 90 fewer calories during that meal.
Professor Brenda Davy, senior author of the study, from Virginia Tech, said it was the first randomised controlled trial looking at water consumption and dieting.
She said the reason water may be so effective is because it fills up the stomach with a liquid that has no calories.
"People should drink more water and less sugary, high-calorie drinks. It's a simple way to facilitate weight management," Professor Davy said."