About 80 per cent of the world's wastewater is discharged into the environment without any treatment, said a UN report released on Wednesday in Durban, South Africa, on the occasion of World Water Day.

While wastewater treatment levels can reach 70 per cent in high-income countries, the ratio in upper-middle-income and in lower-middle-income countries drops to 38 per cent and 28 per cent, respectively, said the UN World Water Development Report.

"In low-income countries, only eight per cent of industrial and municipal wastewater undergoes treatment of any kind," the report said, warning of the increasing damage to public health and environment in Africa, Asia and Latin America.

According to the report, inadequate infrastructure and the lack of technical and institutional capacity and financial resources explain the inefficiency of wastewater management in the low-income countries.

However, said it is vital that these issues are addressed in order to reduce damage to ecosystems and create a culture of water reuse to cope with water shortages.

The direst situations are in the large cities of Third World countries, due to high population growth and the inability to meet minimum sanitation conditions and hygiene.

Under these circumstances, all the water consumed is discharged directly into the closest surface water drain or informal drainage channel without or with very little treatment.

This damages numerous coastal, river and marine ecosystems and triggering the transmission of contagious diseases among people.

"Let's all reduce and safely reuse more wastewater so that this precious resource serves the needs of increasing populations and a fragile ecosystem," chair of UN-Water Guy Ryder said.

By 2030, the UN expects to halve the proportion of untreated wastewater and increase safe water reuse worldwide.