"Water-related diseases kill a child every eight seconds," U.N. Secretary-General Kofi Annan said in a statement for the annual day set aside since 1972 to take stock of the state of the planet.

"One person in six lives without regular access to safe drinking water. Over twice that number - 2.4 billion - lack access to adequate sanitation," he said.

The United Nations says the world must do far more to meet goals of halving the proportion of people who lack safe drinking water and sanitation by the year 2015, part of an overall drive to halve global poverty.

"If we are to meet the commitments...the world will have to spend up to $180 billion annually, more than double what is being spent today," said Klaus Toepfer, executive director of the U.N. Environment Programme.

The United Nations says ordinary citizens can also do their bit with simple measures like plugging leaks at home, collecting rainwater, turning off the tap when brushing their teeth or hosing their car on the lawn rather than on the drive.

IRAQ WAR COST MORE

Lebanon's Prime Minister Rafik al-Hariri, whose country is the main host of this year's event, said the budget of the U.S.-led war on Iraq exceeded the cash needed to alleviate the plight of people suffering from water shortages.

"A fraction of the budgets spent on arms would be enough to eradicate poverty, diseases, malnutrition and protect the environment," he said.

In China, the world's most populous country, the government said it planned to invest more than $30 billion over the next few years to fight water pollution and help relieve shortages.

"China is a country that still lacks water resources, and the problem of water pollution remains severe," said Xie Zhenhua, minister of the State Environmental Protection Administration.

But environmentalists reiterated concern over China's Three Gorges Dam - the world's largest hydroelectric project - which China began filling up on Sunday after a decade of work. It is meant to tame the river whose annual floods have killed 300,000 people in the last century alone.

The WWF environmental group said 1,700 dams planned around the world would suck rivers dry and give few benefits to people most in need. "A growing number of rivers now rarely reach the sea, such as the Colorado River in the United States and Mexico and the Yangtze River," it said.

In Bangladesh, where water can often be both a blessing and a curse, the government launched a tree-planting drive that it said aimed to turn the country into a "garden of green" by 2015.

The United Nations says water is the world's most precious resource and the basis of life. European and U.S. space probes are heading to Mars this year to seek evidence of water - a sign life might have existed on the red planet.