Leonardo DiCaprio has signed a petition urging US President George W. Bush and other world leaders to commit to a legally binding UN treaty which declares clean water as a basic human right.

Speaking on World Water Day last week, DiCaprio said: "We are here to help raise awareness about what is one of the greatest challenges facing humanity today."

DiCaprio then screened "Water Planet", a short film he helped produce which highlights the need to conserve the world's limited supply of fresh water and provide greater access to it for people worldwide, reports femalefirst.

The 30-year-old "Titanic" star was presented with the lifetime achievement award at the Santa Barbara International Film Festival last month.