One of the main issues at the forthcoming water conference in Kyoto is the issue of human waste disposal.
By Alastair Lawson
BBC correspondent in Bangladesh
A growing number of academics argue that the traditional Western sewage method is no longer sustainable.
Good sanitation is sometimes hard to find in Dhaka
Earlier this week the incoming president of the World Water Association, Michael Rouse, called for plans to build sewage works for the 1.2 billion people in the world who currently live without fresh water and sanitation to be scrapped.
He said sewage pipes are too expensive and too often drain into and pollute water courses.
Instead, he suggests the world should revert to using human solid waste as compost and fertiliser and allow liquids to drain into the ground.
Mr Rouse said that it is going to be almost impossible to meet the UN target of halving the number of people without fresh water and sanitation by 2015.
He argued that the focus should be on community-led programmes which are more environmentally friendly and use less water, such as dry and low water toilets.
That is already happening in many parts of South Asia, including Bangladesh, where aid agencies estimate that only around 20% of the country's population of 130 million people have access to proper sanitation.
It's not environmentally or financially sustainable
Water Aid, Bangladesh
"The Western way of going to the toilet is an incredible waste of water resources," says Timothy Claydon, country representative of Water Aid Bangladesh.
He added: "Because it involves piping clean water to someone's home, pouring it into a white ceramic bowl and then flushing the dirty water away with more clean water, it's not environmentally or financially sustainable."
Mr Claydon says that in South Asia the infrastructure does not exist to support such a system.
He says the priority instead should be dealing with the problem of open defecation, a practise which Water Aid and other aid agencies want to be replaced with fixed-place defecation.
But they face a huge task. Over 85% of homes in rural Bangladesh do not have access to any form of latrine, which leads to numerous health problems.
Collecting clean water is often difficult
Water Aid and its partners in the country are encouraging the construction of latrines which use minimal water, while also allowing the faeces to be used for organic compost.
To do that, Mr Claydon explains, requires specially designed toilets where the faeces and urine are separated at source.
Water Aid and other aid agencies in the country are building such toilets all over the country.
Mr Claydon says affluent northern countries are now so familiar with water-borne sewage systems that it will take a long time before there is any significant change in attitude.
"But in South Asia flush toilets for many people are not part of the culture - which means that in 20 years time their method of human waste disposal could be a lot more environmentally friendly," he adds.