By Imogen Foulkes BBC correspondent in Geneva

Some 4,000 children die daily from illnesses caused by unclean water

A new report reveals that more than 40% of the world's population does not have even the most basic sanitation.

More than one billion people have no access to clean water sources, the document adds.

The report was prepared by the UN's children's fund, Unicef, and the World Health Organisation to assess progress towards reaching millennium goals.

A key development goal is to cut by half the number of people without clean water and sanitation by the year 2015.

We have to act now to close this gap or the death toll will certainly rise Carol Bellamy, Unicef UN water report (1.85MB) Most computers will open PDF documents automatically, but you may need to download Adobe Acrobat Reader. Download the reader here

The report makes depressing reading.

If things continue as they are, half a billion people will still have no sanitation 11 years from now.

And while the world is on target to meet the clean drinking water goals, population growth will probably outstrip the improvements.

This would leave 2.4 billion people drinking unsafe water in 2015.

The report also says:

• 1.8m people die each year from diarrhoeal disease
• Over 40 billion work hours are lost in Africa to the need to fetch drinking water
• There has been progress - an estimated 1.1bn people now have better access to water than 12 years ago.

Political will

Unicef points out that it is the young who suffer most from continuing shortages.

"Around the world millions of children are being born into a silent emergency of simple needs," says Carol Bellamy, Unicef's executive director.

WATER FACTS: THE BIG PICTURE Click below for a statistical view of the world's water

"The growing disparity between the haves and the have-nots in terms of access to basic services is killing around 4,000 children every day and underlies many more of the 10 million child deaths each year. We have to act now to close this gap or the death toll will certainly rise."

Rural regions in Africa and Asia are worst affected, but the global trend towards urbanisation is also putting more of a strain on water services in cities.

Unicef and the WHO want this report to be a wake-up call to world leaders.

Achieving clean water and sanitation for everyone will take more than money, they say.

A clear political commitment to the universal right to water is needed too. The report warns that the failure to act will have severe consequences.