What impacts on metabolism are likely from the 6x increase in water consumption by Americans at restaurants since the 1950s?
As mentioned by nico in his comment, this infographic is very misleading in that it presents quite uninteresting data in a way as if it was a sensation.

It claims the average meal drink has been soda which has increased by 6 times in size. Then it claims most of the volume is water. This is of course true. But while a substance solved in water barely increases its volume, it can still make a difference - soda and water are completely different things and the important statistic to look at here is not the amount of water drunk, but rather the fact that it is soda. Where I live, soda usually contains around 27g of sugar per 240ml (8oz) which is 9% of the GDA. So according to this data, people consume half their energy needs of that day with the drink they get in their restaurant meal.

The other statistic is about calories per ounce of the food. What sense does a statistic about that make? The only relevance of the calorie density of food would be the effect on how well it is digested, and for that only a calorie number isn't really helpful. The relative ratios of fibre, carbohydrates and fats would be much more useful in that case. The only interesting statistic here is that meals have almost doubled in size. The fact that the volume of meals has increased much more hints that there is a higher portion of less calorific foods, such as salads.

Impact on metabolism? Hard to say, this is a statistic about what people eat at restaurants, which is not really something that you expect to reflect their refular diet. It doesn't tell you anything about their general lifestyle, which would be the relevant statistic for effects on metabolism. If you only look at restaurant meals, those could look really unhealthy but on the larger scale, people balance it out in their every day diet and general lifestyle. If you had an additional statistic that shows that people actually eat a significiant amount of meals at restaurants, and they're the kind of meals described by the infographic you gave, that would have some implications.