Royal Philharmonic Orchestra plays Katy Perry song using water glasses

The musicians of the Royal Philharmonic Orchestra swapped their violins and flutes today for water glasses. And if you're keen-eared you may have noticed that they also dropped Mozart and Beethoven - in favour of the likes of Katy Perry.

The special performance on the South Bank - dubbed the "H2 Orchestra" - was in benefit of the charity Water Aid.