About one billion people live in slums and the highest concentration of them can be found in Asia.
As part of our Urban Planet series we travelled to the Philippines where about 20 million people live in slums.
One tenth of slum dwellers live in the capital Manila, in neighbourhoods like this one in the Tondo District.
Tondo is one of the oldest areas of Manila, and dates back about 1,000 years.
But the past has been erased by the present. Today it's one of the most densely populated places on earth. There are 80,000 people per square kilometre.
The United Nations says many of them lack adequate water, housing, sanitation, education, health and employment.
Chairman Tom was born and brought up in Tondo, and runs a community of about 4,000 slum dwellers there.
He has six children, and according to Tom "everyday is a struggle".
He sells water for a living and he also makes US$40 a month from renting out property that he built on government land.
"What I did is illegal," says Chairman Tom. "But I have to help my people because 90% of them are much worse off than me".
Jemma, a single mother, lives alongside the bridge in Tondo.
She and her four children live in a tiny room with no water, no electricity and no sanitation.
Jemma washes clothes to make a living. None of her children go to school and her 14-year-old daughter is already working.
"I sometimes get angry with myself because I cannot provide for my children," says Jemma, who starts to weep.
Estella and her husband Cricencio are an elderly couple who moved to Tondo slum from the countryside 20 years ago.
They have seven children and they live at the end of an alleyway.
"I have spent many sleepless nights worrying about the threat of fires," says Estella.
Her husband Cricencio has another major worry. "The land that we live on is owned privately. We have no contract, no rights, nothing," he laments.
Alicia's house is a two minute walk from Estella and Cricencio's, and she is one of the lucky few who was given rights to her land by the government who once owned it.
"I have the deeds," beams Alicia, a single mother with two children. But her smile fades as she reflects on the reality of living in the slum.
"I live about 20 metres from the river," says Alicia. Every year when the typhoons come, my house gets flooded, and sometimes I am knee deep in water.
The river which runs through Tondo is a great source of entertainment for the many young people who live in the slum.
Children spend hours swimming in it, but parts of it are choked with garbage. Some of the slum dwellers, like Estella, admit that they throw throw excrement in, because they have no toilet.
The river is so polluted that the United Nations says it poses a serious risk to health.
A woman is fast asleep on a table in the alleyway underneath the bridge.
She is oblivious to the constant sound of children at play or doing house work.
The government has admitted that the population is growing at an alarming rate and the United Nations says the Philippines has one of the highest rates of population growth in the region.
The average family size is six.
Chairman Tom says some things have improved.
There are health clinics and this year electricity was brought in. Unlike the Mayor, Tom believes in family planning.
"That's why we have programmes here," he says.
As a group of children play outside Chairman Tom's house, he admits that the number of kids is a problem.
But this is just one of a number of worrying trends in Manila. Chairman Tom instances lack of employment and the ownership of the land.
Despite the obstacles he remains upbeat. "This is what God has given me," says Chairman Tom. "And this is my home."