The dripping scaffold of industrial piping looked anything but temporary and was barely hidden from the street, but the men in charge were still edgy.

As they kept an eye out, tanker lorries queued to be pumped full of liquid cargo and then cruise through Karachi's streets delivering to thirsty customers.

For a couple of minutes, the so-called tanker mafia were happy to show off one of their illegal hydrants in the west of the city, before becoming jumpy and insisting I left.

For all the caution, one might suspect their contraband trade involved something more exotic than water.

But in a parched city growing at a runaway rate, water is big black market business.

Organised crime gangs have their tentacles in almost every form of business in Pakistan's mega port. From land and housing to smuggling and drugs, powerful mafias seek to make a profit out of everything.