According to the Economist in an article dated Aug 26, 2010:
"CONSUME more water and you will become much healthier, goes an old wives’ tale. Drink a glass of water before meals and you will eat less, goes another. Such prescriptions seem sensible, but they have little rigorous science to back them up.
Until now, that is. A team led by Brenda Davy of Virginia Tech has run the first randomised controlled trial studying the link between water consumption and weight loss. A report on the 12-week trial, published earlier this year, suggested that drinking water before meals does lead to weight loss. At a meeting of the American Chemical Society in Boston this week, Dr Davy unveiled the results of a year-long follow-up study that confirms and expands that finding."
The article concludes: "Moreover, the effect seems to be long-lasting. In the subsequent 12 months the participants have been allowed to eat and drink what they like. Those told to drink water during the trial have, however, stuck with the habit—apparently they like it. Strikingly, they have continued to lose weight (around 700g over the year), whereas the other participants have put it back on."