The first Victorian Mains Replacement project to be rolled out will be based in the area surrounding St. Pancras station.
This will be followed by replacement works in the Bloomsbury area of the capital in November. Both of these projects are expected to be completed by 2008.
The biggest of the schemes will be in the West End, costing £35M and starting in January 2007, due to complete spring 2009.
The fourth and final scheme will be in Finsbury, north London, commences early 2008.
A Thames Water spokesman said: 'We need to target areas that are critical in bringing the leakage levels down.'
Thames had already planned for this work to go ahead before it was last week forced by the water regulator to spend an extra £150M on fixing leaks in the capital (News last week).