Bottles of water are being handed out by Severn Trent after its pumps at Mythe Water Treatment Works in Tewkesbury, which serves the towns of Gloucester and Cheltenham, south west England, became engulfed in flood water.
About 70,000 properties are without water, and as many as 140,000 may be affected, a spokesman for the water utility said.
It could be days before pumps are working again, and flood water are expected to continue rising, he told the BBC.
People living in Cheltenham are being urged to use water sparingly as only about 20 hours of supply are left.
Prime Minister Gordon Brown is expected to visit a flood stricken area of western England on Monday to see the damage and recovery efforts.
In south-east London 175,000 people were warned to boil their tap water after torrential rain caused flooding at Sutton and East Surrey Water's Cheam treatment plant and affected the water supply.
The Environment Agency issued nine severe flood warnings on Monday with large parts of Worcestershire, Gloucestershire and Warwickshire remaining under water as more than 1,000 people had to spend a second night in emergency shelters.
The Environment Agency has been criticised for its speed of response to the floods, but Environment Secretary Hilary Benn praised the public body's work as well as the efforts of the emergency services.
"We just have to recognise the intensity of the volume of water that's come down and that has resulted in flooding that, even with the best defences in the world, would in some cases have been overtopped," Benn told the BBC.
"The Environment Agency are doing a good job but we need to recognise the scale of the emergency that they are having to cope with, as are local authorities and the fire services."
