About 2.5bn people around the world lack access to safe, affordable sanitation, and some 1bn are forced to defecate openly in public places, according to the United Nations.
World Toilet Day on Monday raises awareness of the serious nature of this problem.
More than 2.7m people die each year because of a lack of sanitation - most under age five, Catarina de Albuquerque, the United Nations Special Rapporteur on the human right to safe drinking water and sanitation, told reporters in Geneva last week.
"Access to sanitation facilities around the world, more than any other service, provides a window into the vast difference between the 'haves' and the 'have-nots'," said de Albuquerque.
One in three women worldwide have no access to a decent toilet, increasing their risk of illness, harassment and even attack, says the NGO WaterAid.
People living in impoverished conditions suffer the most from unsanitary conditions and a lack of proper toilet facilities. Disease such as cholera, typhoid, and hepatitis A are easily spread when people defecate in the open, says the World Health Organization.
An estimated 80 per cent of untreated wastewater in developing countries flows back into lakes, oceans, and drinking water sources. This is a major cause of diarrhoea among children.
The scale of the problem is not being adequately addressed, health officials say. At current rates of progress it will be 350 years before everyone in Sub-Saharan Africa gets access to safe sanitation, says WaterAid.
"With around 2,000 children under the age of five dying every day from diarrhoea, brought about through unsafe sanitation, dirty water and poor hygiene, we need to step up the global efforts to tackle what is the second biggest killer of children worldwide," Barbara Frost, WaterAids's chief executive, told Al Jazeera.