thought of the idea of sneaking in a container for water at a rave (to avoid paying 5 bucks for a goddamn arrowhead bottle) and googled collapsable water bottle. comes in up to a liter size and looks like it could be folded up enough to be smuggled in. AND is only 2 bucks more than what theyd charge you for water at a rave!
http://www.paddlesportsonline.com/ssrs/detail.aspx?ID=191
http://www.paddlesportsonline.com/ssrs/detail.aspx?ID=191