The Prix Pictet is a new global photography prize created to draw attention to the issue of sustainability. Its first year takes the theme of water, a precious commodity, too often polluted, too often out of reach. Francis Hodgson, chairman of the Pictet jury, discusses the importance of photography, and takes us through a selection of this year's shortlisted entrants

It was Mark Twain who said: "If you have nothing to say, say nothing." Photographers, as well as writers, would do well to heed this maxim. Indeed, the medium of photography has been so overwhelmingly successful that photographers sometimes struggle to find something we don't already know.