Harold McGee, a fabulous scientific food writer, just wrote an article in the NY Times about how to save millions annually by cooking pasta in less water. Less water = less energy to heat the water. The same principle works in washing machines; the side mounted washers use less hot water and that is one of the principal mechanisms by which they use less energy.
McGee’s point that it might save $10-$20 million annually is right, but this comes out to <10cents per year per person, which turns out to be pretty small potatoes. Still, there’s no reason to waste energy when one doesn’t need to. And most people I know hate the arduous task of dumping pasta water.
see the article: http://www.nytimes.com/2009/02/25/dining/25curi.html
