There are a number of theories out there amongst the scientists, some of which are solidly backed up by the research, others which are more hypothetical.
These seem to be the most likely explanations:
Feeling Fuller
Test meal studies have shown that drinking water prior to and during meals increases satiety and changes in feelings of satiety are associated with a lower overall calorie intake which, in turn, leads to weight loss.
Increasing Metabolic Rate
Water drinking may provide thermogenic increases metabolic rate. A faster metabolism burns more calories.
Mobilizing Fat Stores
Water is essential for metabolising stored fat into energy, so much so, that the body’s metabolism could be slowed down by even fairly mild levels of dehydration. The slower your metabolism, the harder it is to lose weight.
Drinking Less Calories
The more water you drink, the less need you have for drinks that contain calories. The fewer calories you consume, the more weight you