More than one billion people worldwide have no guaranteed access to water and more than two billion are without adequate sanitation, according to a report released on Wednesday by an anti-corruption organization.

Transparency International, a German-based non-governmental organization that focuses on corruption around the world, says that by 2025 more than three billion people could be living in water stressed countries.

The claims are made in the group's annual report, called Corruption in the Water Sector, which was released in Berlin and at the United Nations in New York on Wednesday.

It provides a snapshot of corruption-related events in 35 countries and regions around the world.

"Water is a resource without substitute. It is paramount to our health, our food security, our energy future and our ecosystem. But corruption plagues water management and use in all these areas," said Transparency International chair Huguette Labelle.

Most health problems attributable to water quality

Corruption in the water sector threatens billions of lives as it makes water undrinkable, inaccessible and unaffordable, the report says.

In developing countries, the report argues, about 80 per cent of health problems can be linked to substandard water and sanitation services, claiming the lives of nearly 1.8 million children every year.

Students suffering from water-related ailments around the world miss an estimated 443 million school days every year, the report suggests. For the poor, the loss of an education turns into lost economic opportunities, making the cycle of poverty increasingly difficult to break.

When corruption is factored in, the report says the consequences for development and poverty reduction are dire.

For instance, corruption can increase the cost of connecting a household to a water network by more than 30 per cent, the report says.