US President Barack Obama tries the bicycle-powered emergency water-sanitation station, created by high schoolers Payton Karr and Kiona Elliot from Oakland Park, Florida in the East Garden of the White House, during the White House Science Fair, in Washington, DC, USA, 22 April 2013. The fair celebrates the student winners of a broad range of science, technology, engineering and math (STEM) competitions from across the country. EPA/AUDE GUERRUCCI / POOL