Not being able to find a toilet can be an embarrassing, even agonising, experience – and one which most people have been through.
But for the forty per cent of the world's population who still do not have access to toilets at all, the consequences can be fatal: 1.8 million people die annually as a result of poor sanitation facilities, says the Swiss aid agency Helvetas.
Where there are no adequate toilet facilities and people are forced to relieve themselves in the open, contaminated water easily spreads disease.
2008 is the UN Year of Sanitation, and it is worth remembering that until comparatively recently, people in the West were faced with the same problem, and that it was fatal here too.
In the 19th century three major waves of cholera swept through Europe, leaving hundreds of thousands dead, and doctors helpless.
And yet even when the relationship between contaminated water and disease was understood, it took many years before adequate toilet facilities became the norm.
Older houses in the poorer quarters did not include space for any sort of toilet; people simply went outside. As the health risk became apparent one response was to create a dense network of "public conveniences" for people who lived in buildings where it would have been difficult to install even shared sanitation.
Tackling the problem
The euphemism indicates another problem: bodily functions were not to be talked about. As a result, public toilets were often disguised or even hidden away, sometimes built underground.
Easy to find, but out of the public eye, many were taken over for other uses. Some have become places for sexual pick-ups or for drug dealing. Today vandalism is a common problem. It's a vicious circle: ordinary people start avoiding them, and they fall into greater disrepute.
Switzerland's biggest city, Zurich, is making a determined effort to change the poor image of the public toilet.
It is proud of its facilities; it wants people to think about them and talk about them and express their opinions. Its address and phone number are posted in every one.
Each one also bears the little blue ZüriWC logo, to create a corporate identity amid the plethora of styles.
ZüriWC keeps the public informed on its website of what is going on where. Old facilities are being renovated and new ones built.
"There's a growing need," Urs Brunner, head of ZüriWC, told swissinfo. "You hear it everywhere, in playgrounds, parks, sports areas, people expect to be able to go to the toilet."
Bright and high-tech
Today, the 94 facilities looked after by ZüriWC range from discreet late 19th buildings in stone, to 21st century ones in brightly coloured synthetic material. Six are listed historical monuments; others are the latest design in compact unisex facilities, made of easy-to-clean chrome with integrated, automated hand-washing facilities.
It is important to ZüriWC that the toilets should fit in with their surroundings, even though the older type is more expensive to maintain, Brunner explained.
Whenever toilets are built or renovated, disabled facilities are included. People with disabilities can apply for a eurokey, which will open toilets in all participating European countries.
Without a key, these special facilities cost one franc. Otherwise public toilets in Zurich have always been free and will remain so, said Brunner.
He believes that access to a well cared for toilet facility is everyone's right. Many WCs which once felt insecure have been improved: the entrance has been moved, perhaps, so that it is more visible, or extra lighting has been installed.
Then and Now
The oldest WC still standing in Zurich was built in 1898, although the first urinals had appeared in the late 1870s. After long discussion, the first public WC for women opened in 1893 – to much protest. Women found it rather expensive; men thought women should be staying at home.
Most of the earliest facilities were permanently staffed; today only five have attendants on duty all the time. Then as now, one of their jobs was keeping the toilets clean. Where there were no attendants, special cleaners were recruited.
If today cleaning toilets is a proverbially undesirable job, a hundred years ago it was seen as an ideal way for local women to eke out the family income with work that could be done close to home.
Today the latest toilets are self-cleaning – sometimes alarmingly so to the uninitiated, who are taken aback when the toilet seat springs up and triggers the flush.
It's a far cry from the days when lack of proper facilities spread disease and death.
The International Year of Sanitation provides a salutary reminder that it's a far cry too from the situation prevailing in many developing countries today.
swissinfo, Julia Slater in Zurich
Sanitation and Health
Forty per cent of the world's population do not have access to toilets.
Every year 1.8 million people die as a result of poor sanitation.
Disease spreads when faecal material seeps into the groundwater or flows into streams from where people take their drinking water.
Cholera, typhoid and dysentery are three diseases caused by drinking contaminated water.
In the 19th century hundreds of thousands of people died in Europe in three major waves of cholera.
Until the late 19th century it was widely believed that cholera was carried in the air.
The cholera bacillus was discovered in 1854 by the Italian Filippo Pacini but he was ignored; it was rediscovered in 1883 by the German doctor Robert Koch.
Public Health acts and the installation of sewage and sanitation facilities put an end water-borne diseases.