The problem with "solutions" like this is that they don't really fix the problem where it lies. Weight gain is attributed to caloric surplus, there's no two ways about it.

Drinking water before a meal will help you feel a little fuller and ultimately, eat less. People ignorant to nutrition will begin to use this as a free pass to eating even more poorly.

If you really take a step back and look at this, what they are suggesting is filling up with less calorie dense foods (water being the ultimate example), preferably with a high satiety index (here's a list: http://www.mendosa.com/satiety.htm).