Jakarta is sinking faster than any other big city on the planet. 

Some coastal districts in Indonesia's capital have sunk as much as four metres in recent years. 

The main cause: Residents are digging illegal wells and draining the underground aquifers on which the city rests. 

About 40 percent of Jakarta now lies below sea level.  

If its 10 million residents are to remain there, the city must find alternative sources of water and raise its seawall.