More than half of the world's population do not have access to safely managed sanitation, the United Nations revealed to mark World Toilet Day.
Of those, three billion lack basic handwashing facilities and 673 million still practise open defecation, the UN said.
Lack of access to hygienic toilet facilities can have deadly consequences as inadequate sanitation is estimated to cause 432,000 diarrheal deaths every year — of whom nearly 300,000 are children under the age of five.
Other diseases linked to the sanitation crisis include cholera, dysentery, typhoid and polio which are spread through water contaminated by human waste.
According to the latest figures from the World Health Organisation, at least two billion people use drinking water contaminated with faeces. The body also estimates that by 2025, half of the world's population will be living in water-stressed areas.
The problem primarily impacts least developed countries where 22% of health care facilities have no water service and/or no waste management service. People fleeing war or strife are particularly vulnerable as they are likely to gather in camps with sparse infrastructure.
But it also exists in richer regions including Europe. Last year, more than a quarter of Romania's population reported not having access to an indoor flushing toilet, Eurostat, the European Union's official statistics agency, calculates.
That figure stood at 15.3% in Bulgaria, 10.6% in Lithuania and 9.9% in Latvia — far above the European Union's average of 2.1%.
On top of the health, environmental, and safety implications — girls and women spend 266 million hours every day finding a safe place to go, according to Water.org — the sanitation crisis also has a hefty economic price. The UN estimates that loss of productivity to water and sanitation-related diseases costs many countries up to 5% of Gross Domestic Product.
The problem has attracted a lot of attention and capital. The Bill and Melinda Gates Foundation, created and led by the American billionaire, launched the Reinvent the Toilet Challenge in 2011, providing grants to 16 researchers around the world to develop innovative approaches.
Some of the models these scientists worked on include solar-powered installation or appliances that recover nutrients from human waste.
The "waste-to-wealth" idea is of particular interest because of the business opportunities arising from it.
"The business of safe recovery of water, nutrients and energy from domestic and agro-industrial waste offers significant opportunities to generate economic and social benefits to women and unemployed youth, especially in developing countries," Josiane Nikiema, from the International Water Management Institute, said.
Other research strands focus on saving as much water as possible.
Around the world, the risk of droughts has increased because of rising temperatures and no regions are spared. Europe, long considered as having adequate water resources, now has to contend with frequent water scarcity phenomenon because of longer and warmer heatwaves prompting authorities to take punctual water conservation measures.
In South Africa, where severe droughts dramatically depleted water reservoirs this year, signs — including the "if it's yellow, let it mellow, if it's brown, flush it down" — informed visitors about best practices to save water.
But technology could also help.
Researchers from Pennsylvania State University have developed a coating that when applied to toilet would prevent liquids and solids from sticking to the surface of the bowl.
According to their study, published on Monday in the Nature Sustainability journal, over 141 billion litres of fresh water are used globally every day for water flushing. "This is nearly six times the daily water consumption of the population in Africa," they noted.
They found that their sprayable solution would reduce water consumption by 90% compared with untreated surfaces.