Huge tunnelling machines are at work beneath London

Engineers working on the rail link between Kent and St Pancras in London have been siphoning off underground water through boreholes.

The excess water has been trickling into the nearby River Roding and River Lee, but Thames Water tests have shown it can treated for use as drinking water.

Thames Water is now planning to build a pipeline between the boreholes and a new water treatment centre at East Ham.

Ten existing boreholes between Hackney and Barking will also be converted to supply drinking water.

Thames Water estimates the �32m project will provide an extra 20m litres of water a day for east London by 2005.

John Sexton, Thames Water's managing director, said: "Increased levels of development in the area, coupled with the likelihood of up to 700,000 people moving into London by 2016, make water an increasingly precious resource."

A report by Ofwat, the water industry's regulatory body, report last year found Thames Water leaked more than 860 mega-litres per day, a third of its supply.