Is Veganism sustainable?

This is a question that I get more than I would think. Many people seem to be under the idea that if everyone switched to vegetables and grains the price would go through the roof. The other false notion is that if we all went vegan we would run out of water, from watering all these plants. Now  for the first portion of this argument I point to a study done by David Pimentel, professor of ecology in Cornell University's College of Agriculture and Life Sciences said that "If all the grain currently fed to livestock in the United States were consumed directly by people, the number of people who could be fed would be nearly 800 million." Such a boost in supply wouldn't increase the price of our vegan food, it would lower it drastically. The main consumer of grains in the U.S is currently livestock, if we stopped eating them that would free up vast amounts of resources that are currently tied up with our addiction to meat. Part 2 of this argument is this idea that plants take up more water than animals. Lets look at one of the most water intensive crops, Almonds come in at a shocking 1 gallon of water per 1 almond. Now that is a lot of water no question, but lets compare that to a few other animal products. An Egg takes 53 gallons of water, a gallon of milk takes 144 gallons of water (A Funny side note with milk, according to U.S. Dairy report around 95% of the water that is used to produce milk is used to grow cow feed). A pound of chicken flesh? 468 Gallons, a pound of pig flesh? 576 gallons. Now how much do you think a pound of Cow meat would cost us in water? 2,500 gallons, which meats a 15 average steers could float an Aircraft Carrier. Which is an insane amount of water, we really need to look at this and ask our-selves which eating practice is really unsustainable.