Unfortunatley there's no real hard science behind the water thing. According to some research, water consumption might spark the body to produce more heat, boosting metabolism and burning more calories. But the research isn't in depth enough to say for certain. The other argument is that it makes you feel more full so therefore reduces calorie intake or stops you drinking high calorie drinks.
But what is scientifically backed up is that your body needs at least 2L a day (via food with water content, water etc) to function optimally so if you aren't getting that much you need to make sure you at least get that. It will help your skin, your concentration, your general feeling of well being etc.