Pakistan, Sept. 5 -- Pakistan wants to export more rice, textiles, sugar, meat, fruit and agricultural products to the Gulf and beyond. The logic appears compelling. Pakistan needs dollars, agriculture supports millions of livelihoods, the Gulf needs food security, and geography gives us an obvious advantage.

But there is a question almost entirely missing from this conversation: how much water are we exporting with every dollar we earn?

A kilogram of rice leaving Karachi is not simply a kilogram of rice. Embedded in it are land, fertiliser, electricity, labour, logistics - and water. Cotton carries water with it too. So do sugar, meat and fruit.

Economists call this "virtual water": the water consumed in producing a commodity that is ...