Thousands of people in west London were left without water and up to 60 homes were flooded when a mains pipe burst.
Supplies to homes and businesses in Hounslow, Chiswick and Twickenham were affected when the pipe in London Road, Brentford, broke at about 0600 BST.
Thames Water said it began restoring supplies to affected properties by late afternoon.
The firm said work to fix the pipe could take 48 hours and repairs to the road surface could take up to a week.
A spokeswoman for Thames Water said engineers had re-routed water into the area from other parts of the network.
She said: "The burst was on a strategic water main that serves thousands of people.
"We are really sorry to all the customers affected by this incident."
London Road remains closed between Syon Lane and Bush Corner and people have been advised not to walk on the flooded road in case they fall into manholes.
The spokeswoman said they were starting to fix the pipe, and once this is done it would take up to a week to rebuild the road surface.
"A team of Thames Water staff, along with our loss adjusters, have been visiting customers affected by flooding to assess the damage, arrange alternative accommodation where needed and start the process of clearing up and dealing with insurance claims," she added.
London Fire Brigade, who said between 50 and 60 properties were flooded, earlier handed out sandbags to residents to help them stop water flowing into their homes.
Zora Samim, who lives in Lodge Close, near the burst main, told the BBC that people used buckets to remove water from their homes.
"We have tried to put a barrier against it but it's flooded most of the homes here.
"We have got a lot of water in our house at the moment and there's nothing we can do about it.
"In this road alone we have only been given six sandbags, that's it."