Electricity powers the life support systems that keep our cities running. Lights Trains communications even hospitals rely on this invisible force. Without it our cities stop working and lives are at risk.
Food- human life can't exist without it. It's a city's most important source of energy. In New York alone 8 million people consume 10000 tonnes of food every day. Without new supplies cities will run out of fresh food in a matter of days.
The world's cities are growing at a faster rate than ever before. An estimated 75 million people around the world move to an urban area every year. And as our metropolises become more and more crowded architects designers and builders face a constant challenge.
The lifeblood of cities. Its transport links are its veins and arteries. If they're cut -off the city will die. Thousands of people work every day at making it possible for city dwellers to be where they need to be when they need to be there. It's an endless task demanding brain and brawn.
For centuries cities have been built near a freshwater supply. Without it we'd be lucky to live three days. But this most basic human need can be deadly too - get the supply wrong and it can poison us get too close and it can drown us.
Ian White
Producer