The researchers divided 48 inactive Americans, aged 55 to 75, into two groups. Members of one were told to drink half a litre of water (a bit more than an American pint) shortly before each of three daily meals. The others were given no instructions on what to drink. Before the trial, all participants had been consuming between 1,800 and 2,200 calories a day. When it began, the women's daily rations were slashed to 1,200 calories, while the men were allowed 1,500. After three months the group that drank water before meals had lost about 7kg (15½lb) each, while those in the thirsty group lost only 5kg.
via: Lifehacker: Increase Your Water Intake to Accelerate Weight Loss