Jay-Z launched the tour alongside UN Secretary-General Kofi Annan

At the launch of a collaboration with the United Nations, he stressed that young people need to get the message about saving water.

The tour will be followed for a new programme by music channel MTV.

"As I started looking around at ways I can become helpful, it started with water," said the rapper, who is also head of Def Jam records.

"Young people need to know the problem exists," he added.

UN Secretary General Kofi Annan said the world water crisis is "one of the most important issues on the agenda for the United Nations," and that getting Jay-Z involved will help raise awareness.

Water wars

Jay-Z - real name Shawn Carter - said that he had wanted to play music in places he had not been to before.

He highlighted statistics that show more than one billion people live without clean drinking water and 2.6bn lack clean sanitation.

"I figure that once I stumbled upon that, if the information was out and young people knew that these problems exist... we'll get involved," he said.

In March, scientists warned that Africa could be faced with 25% less water by the end of the century because of global warming, scientists have warned in a new report.

There have also been warnings that as populations increase, "water wars" are likely as countries fight over access to supplies.

In June, the rapper announced a boycott of Cristal champagne at his 40/40 Clubs in New York and Atlantic City.