The (left-leaning, liberal, etc.) nytimes has an interesting article on this. A recent study comparing the Hazda people that follow a hunter-gatherer lifestyle with a lot of exercise, show that they burned similar amounts of calories to many more sedentary people. It's unclear that just increasing exercise will reduce someone's weight. http://www.nytimes.com/2012/08/26/opinion/sunday/debunking-the-hunter-gatherer-workout.html

Most of the water usage is not generated from household use, but from agriculture. As a result, the food you eat has much more to do with water usage than anything else (a good reason to be vegetarian): http://www.un.org/News/briefings/docs/2008/080514_Water.doc.htm