Almost a third of people in the world have no access to a toilet, a privation that has dramatic consequences and leads to millions of deaths each year, experts at a water conference said this week.
Children, highly susceptible to hygiene-related diseases, are the main victims.
'Diarrhea resulting from poor sanitation and hygiene is responsible for the death of more than two million impoverished children each year,' the Stockholm International Water Institute (SIWI) said during the World Water Week conference gathering some 2,500 international experts in the Swedish capital.
And the World Health Organization estimates that 80 percent of all sickness in the world is attributable to unsafe water and sanitation.
Yet the problem has not attracted the attention it deserves and is described as the 'orphan child' of the water sector, often underexplored and underfinanced.
'It's one of those untold stories of the development sector,' said Sunita Narain, director of the Centre for Science and Environment in India and a prominent expert at the conference.
'One reason is the taboo part. You don't talk about these issues so easily, it's a private thing,' lamented Johan Kuylenstierna, the director of World Water Week.
But Narain noted with a hint of optimism that governments were beginning to make the issue a priority.
Sanitation and hygiene conditions have wide-ranging implications on society.
They play a direct role on people's overall health, but also on infant mortality rates, poverty reduction, the role of women and girls in society, schooling, the environment, and social and economic development, according to the United Nations.
'Women are most affected by the problem of lacking sanitation systems,' Kuylenstierna said.
Gynecological illnesses and hygiene problems linked to menstruation make girls and women particularly vulnerable.
Many girls do not pursue an education because schools do not have proper toilets or they must share toilets with boys.
Lack of clean water also affects education since many students who fall ill miss classes, the UN said.
The one-third of the population who have no access to toilets, or 2.6 billion people, generate more than 200 million tonnes (220 million US tons) of excrement annually that are neither collected nor treated, presenting a health risk.
Installing toilets would not be very costly, insisted Kuylenstierna, who criticised the lack of political will and action in the field as a 'scandal'.
For each dollar spent on improving sanitation and hygiene conditions, between three and 34 dollars (25 euros) would be saved in the fields of health, education and socio-economic development, according to the UN.
The UN has declared 2008 the International Year of Sanitation, putting the spotlight on public health amid a rise in urban poverty and expanding slums.
'The slum problem is very much a water and sanitation problem,' said Inga Bjoerk Klevby, the deputy director of the UN's housing programme Habitat.
Some one billion people, or one of every six people in the world, currently live in slums, poverty-stricken and overpopulated neighbourhoods that have inadequate infrastructure for sanitation and hygiene.
The trend of urban poverty shows no signs of diminishing: about half of the world's population currently lives in urban areas, a figure that is expected to rise to two-thirds by 2030, Klevby said.