Islamabad, Aug 26 (DPA): Some 3.5 million survivors of the worst floods in Pakistan's history only have contaminated water to drink, which is increasing the risk of water-borne diseases spreading, the UN said.

The floods triggered by heavy monsoon rains a month ago have impacted more than 20 million people. Nearly half of them rely on the assistance provided by the government or international aid organisations.

The UN said Wednesday that its Children's Fund UNICEF had so far been able to reach around 2.5 million people in flood-devastated areas with five litres of clean water per person a day, which is less than the minimum health requirements.

"We are working as fast as anyone could, but this is not enough," said Karen Allen, deputy country representative of UNICEF in Pakistan.

"Millions of people are still faced with the dilemma of drinking contaminated water, putting them at risk of diarrhoeal diseases." The water-borne diseases were already spreading among the people affected by the floods that have swamped around one-fifth of Pakistani land.

According to the World Health Organisation (WHO), 3.2 million people had received medical treatment for diarrhoea, skin diseases, acute respiratory infections and other illnesses in flood-affected areas.

Some 65,000 cases of malaria were reported in the southern provinces of Baluchistan and Sindh, where a second wave of floods was displacing hundreds of thousands of people.

"Lack of clean water leads to poor sanitation, and this is a major concern which leads to heightened risk of disease. Waste is building up," said Paul Garwood, a WHO official. "This awful combination puts people at greater risk for contracting disease."

"Without clean water, people are unable to wash their clothes. If they are in wet dirty clothes for days on end, this may lead to rashes which can turn into more serious ailments," he added.