Fertilizers poison tap water in California

In California's Central Valley, where verdant fields of fruit and vegetables unfurl under sunny skies, the water that feeds them - and flows into taps across the region - contains a toxic and silent poison.

The very same farmers who have tilled and cultivated the earth for decades in one of America's biggest produce regions have also poisoned it, dumping millions of tons of fertilizer, which has found its way into many of the region's aquifers.

Nitrates, a residue left behind by intensive farming, now lurk in the water in a number of communities, many of them poor and rural.