Here are some key facts about the state of the planet's water resources ahead of the 4th World Water Forum which begins in Mexico City on Thursday:

- At least 1.1 billion people, or about a fifth of the world's population, do not have access to safe drinking water. Most of them live in Asia or sub-Saharan Africa.

- The total volume of water on earth is estimated at about 340 million cubic miles of which only 2.5 percent is fresh water.

- Agriculture accounts for some 90 percent of the world's water consumption. Industry and the domestic sector use about 5 percent each.

- The United Nations says that even though the world has plenty of fresh water, the problem of access to the resource is caused by mismanagement and corruption. In many parts of the developing world, about 40 percent of the water is unaccounted for because of leaks in canals and pipes and illegal connections.

- One of the U.N. Millennium Development Goals (MDGs) is to halve, by 2015, the proportion of people without sustainable access to drinking water and sanitation, but the United Nations says this may not be achieved.

- Some scientists say that the risk of violent conflict over water is rising because of explosive global population growth and widespread complacency. The water-scarce Middle East is regarded as the most likely flashpoint.

- The United Nations estimates that it would cost $6.7 billion a year to meet MDG targets on water and sanitation - compared to the $17 billion spent by Europe and the United States annually on pet food.

- At least 2 million people, most of them children, die every year from water-related diseases caused by lack of access to water and sanitation.

Sources: Reuters, U.N. Educational, Scientific and Cultural Organization (www.unesco.org), U.N. Environment Programme (www.unep.org)