Check out how Bonaroo has gotten greener and more sustainable... especially their admirable new way of dealing with water. No festival is perfect yet, but they have come a long way and most of these mega-festivals really blow it on this.
http://www.popmatters.com/pm/feature/109394-bonnaroo-creating-a-sustainable-city/Free & plentiful filtered drinking water plus stainless steel bottles is the way to go. Bottled water is a global menace.