From Powerball.com
"You do not have to be a U.S. citizen or U.S. resident to play Powerball®. Players from jurisdictions where Powerball tickets are not sold, either in the United States or outside the country, when visiting a selling jurisdiction, can purchase Powerball tickets from a retailer licensed or authorized by the selling jurisdiction, if they meet the legal age requirement in the jurisdiction of purchase. Federal and jurisdictional income taxes may apply to any claimed prize money."