With the issue also affecting a second water treatment operation, many customers found themselves disrupted, according to the water company.
Power recovery at Ashford Water Treatment Works, the initial problem source, indicates water supplies should progressively resume throughout the affected areas.
The company said: “We’re really sorry for the worry and inconvenience this will have caused.
Fixing the problem is a “top priority,” it added.
“We’re working hard to get things back to normal as soon as possible, but it’s likely to take some time for the supply system to refill and for water to fully return to the whole area.”
Thames Water said the problem was affecting its customers in the west London area, with SW, TW and W postcodes.
Schools and libraries across the area have been forced to close by the water issues.
Mayor of London Sadiq Khan called on Thames Water to provide “the answers Londoners want about why this has happened and how to ensure it does not happen again”.
MPs have called on Thames Water to resolve the issue.
Sarah Olney, Liberal Democrat MP for Richmond Park said on X, formerly known as Twitter: “I’ve just learnt that areas across the constituency will have no, or low, water pressure today due to a power supply issue at the Ashford and Hampton Treatment Works.
“I’ve reached out to Thames Water to ask when residents can expect the issue to be resolved.”
Munira Wilson, the Liberal Democrat MP for Twickenham, wrote: “I’m hearing some schools locally aren’t opening this morning due lack of water.
“Our supply in Whitton also stopped this morning Thames Water need to sort this soon!”
Private girls’ school Lady Eleanor Holles (LEH), in Hampton has sent its pupils home because of the water problems.
In a statement posted on X, it said: “Power supply issues at Thames Water have affected water supplies across West London causing low pressure or no water.
“As a result, LEH pupils are being sent home for the rest of the day. Parents are asked to check emails for updates.
“School is expected to reopen tomorrow.”
Some libraries in Richmond are closed because of the problems.
Richmond upon Thames Libraries posted on X to say: “Please get in touch with your local library to see if they are open before visiting. We apologise for the inconvenience caused.”
A Thames Water spokesperson said: “We’re really sorry to customers in West London who are experiencing low pressure or no water.
“We’re working hard to fix the issue, which was caused by a power supply problem which has affected our water treatment works in west London.
“We’re now back in power and expect water supply to return across the day.
“Getting water supplies back on is our top priority and while our team work on this we’re identifying everyone in the affected area who has pre-registered with us as having special requirements, such as being medically reliant on water, so we can get in touch and make sure we give them the help and support they need.”