A young girl jumps over a stream filled with waste-water which flows through the slum area of Ajeromi-Ifelodun in Lagos, Nigeria. WaterAid/ Tom Saater
For the first time in our history, more than half the world's population is living in towns and cities - a number which is expected to increase to two-thirds by 2030 as people increasingly move from rural areas in the hope of a better income and lifestyle.
This means that if we are to create a healthier, more sustainable planet, we need to focus our attention on cities.
One person in every five living in a town or city today does not have access to a safe toilet, a crisis that threatens the health and security of all city dwellers.
State of the World's Toilets
This World Toilet Day, WaterAid has examined the State of the World's Toilets in cities - an analysis showing which countries, towns and cities which have made most progress to provide their residents with decent sanitation, and those that are struggling.
The findings are startling: India, for instance, is still struggling to provide sanitation for its urban-dwellers, despite strong government focus on Swachh Bharat - the Clean India Mission - in part because its cities are growing at such break-neck speed. Ghana, a country which is otherwise making good headway, is struggling to keep pace with the need for decent sanitation which will hold back its visionary ambitions for progress.
While China leads the way in progress on providing sanitation to its urban population, there are other nations on the top 10 list including Pakistan and Cambodia which have also made impressive progress, through concerted political will and targeted financing and, in some cases like in Pakistan's enormous Orangi Town slum, through residents taking on the task themselves.
Sanitation workers: unsung heroes
We've also taken a look at some of the sanitation workers whose toil and dedication ensures their corner of a city is made healthier for all - from a sewer-line builder in Pakistan to a latrine attendant in Liberia to the head of maintenance at the new public toilets at a teeming bus terminal in Dhaka, Bangladesh.
Abdulla Saidu is the manager of the local public toilet in Nima, one of the poorest parts of Accra. WaterAid/ Geoff Bartlett
Pressing health crisis
With more than 2.3 billion people in the world still waiting for safe, private toilets, this is truly a pressing health crisis; some 315,000 children under five die each year of preventable diarrhoeal illnesses linked to dirty water, poor sanitation and poor hygiene. But it can be hard to convince politicians to treat this crisis with the urgency it deserves. It's much more exciting to open a new school, road, or hospital than a new set of community latrines - even if the use of those schools and hospitals is compromised because they are without proper provision of safe water and decent toilets.
Sanitation is the bedrock of public health, and essential to creating healthy, thriving, productive cities. We hope this year's report will shed some light on where the hard work needs to happen, and on some of the heroes in this daunting challenge.
Everyone living in urban areas, including those in informal settlements, has the right to have a toilet to ensure their health and that of their communities are protected.
Increased investment and priority
We need to see increased investment that is better spent, from international donors and developing-world governments alike, to deliver sanitation, clean water and good hygiene for all. We need to see better coordination and shared drive from governments, city planners, NGOs, the private sector, service providers and residents - to make these services happen and keep them running. And sanitation workers, the unsung superheroes that are keeping us all safe, should be recognised and celebrated for the important role they play in keeping city dwellers healthy and productive.
In short, this World Toilet Day, we are calling on global leaders to deliver on their promises to meet the UN's Global Goal 6 to ensure universal access to safe water and sanitation. The health and well-being of our urban world depends upon them.