The chance of a hosepipe ban being introduced in London by August is likely, Thames Water has said.
Thames Water has replaced 140 miles of pipes
Supplies of water are being drawn from a contingency reserve for the first time in eight years because of low levels of rainfall.
The below-average rainfall over the past eight months has equated to the driest period since 1976.
Thames Water said it had replaced 140 miles of mains pipes in an attempt to preserve what water there was.
The company plans to replace a further 850 miles between now and 2009 to stop leaks.
Richard Aylard, of Thames Water, told BBC News: "We haven't had a hosepipe ban in the Thames area for the past 15 years. A lot of people have worked hard to make and maintain that situation and we hope we can prevent one this time but I have to say it's looking more and more likely.
"It depends how much rainfall we get and it depends how much water we can draw from elsewhere, but we think there's a realistic possibility of a hosepipe ban by August."