GENEVA — The world has significantly reduced the number of people who lack access to clean drinking water, but far more work needs to be done to help the 2.5 billion people worldwide who lack basic sanitation and suffer as a result, the U.N. said Thursday.

The world's poor face a much higher risk of infection and diseases such as cholera because they usually are left with no choice but the bush or other open places to relieve themselves.

A joint report by UNICEF and the World Health Organization said 70 percent of the people living with broken down or nonexistent sewage systems are in Asia and 22 percent in sub-Saharan Africa. Some 1.2 billion people have no sanitation at all, and use trees, fields and other outdoor places instead.

"About 5,000 children die every day from simple diarrheal diseases," said Clarissa Brocklehurst, chief of UNICEF's water and sanitation unit. Most of the deaths are caused by inadequate sanitation, she said.

Governments have been slow at reducing the number of people living without decent sanitation, despite pledging at the beginning of the decade to cut that figure in half by 2015.

But countries are making progress in providing more people with safe drinking water.

Around 13 percent of the world's population, or 884 million people, lack safe drinking water. That number has been almost halved since 1990, the agencies' 58-page report said.

Sub-Saharan Africa is the worst region, with people often drinking from wells, springs, rivers and lakes that are not protected from outside contamination.

The agencies predicted that more than 90 percent of the world's population will likely have access to safe drinking water by 2015.