Thousands of homes across south London and Surrey were left without water on Monday due to a burst water main.
Thames Water has said that supplies have now been restored after engineers isolated the broken pipe in West Molesey, Surrey, and were working on a permanent repair.
The company apologised for the outage, and said that the repair requires a fabricated part and the location of the burst makes this process complex.
Many customers are likely to experience lower pressure than normal and for supply to be intermittently affected during busy periods until the pipe has been fully repaired.
It is estimated that up to 15,000 properties were initially affected by the issue, with that number falling to around 6,000 as work on the broken pipe began.
The affected post codes have been located across Kingston upon Thames, Merton, Richmond upon Thames, Sutton and Wandsworth in London, as well as Elmbridge and Spelthorne in Surrey.
A bottled water station has been set up at Sandown Park Racecourse on Monday afternoon for customers who are still experiencing low water pressure or no water.
Some schools and nurseries in the impacted area were forced to shut because of the fault.
The Holy Cross School in New Malden, south London, said: “Due to a local water supply issue affecting the school site this morning, we have taken the decision to close the school today.”
Esher Sixth Form College, Thames Ditton Infant School and Long Ditton Infant and Nursery School also said they were shut for the day because of the issue.
Monica Harding, MP for Esher and Walton, Surrey, said: “We need an urgent response from Thames Water to get water supplies back on as soon as possible and to protect vulnerable communities.
“Once the water is flowing again, we need to establish exactly what happened and why.
“My worry is that decades of underinvestment in our infrastructure and poor regulation may be causing incidences like this.”
Luke Taylor, MP for Sutton and Cheam, said that Thames Water was "no longer fit for purpose".
He added: "Every day Thames Water loses 228 Olympic-sized swimming pools worth of water through leaks.
"Most of the time this slow drip of leaks across London costs us money and wastes energy, but today the huge burst pipe in West Molesey means carers can't wash their loved ones, businesses are shut and schools are closed."
Liberal Democrat leader Sir Ed Davey said: “Thames Water is already the worst water company in England and Wales for leaky pipes – losing an average of 592 million litres every single day,” he said.
“Meanwhile, 28% of customers’ bills goes straight to servicing the company’s debt, not fixing the crumbling infrastructure that is now failing them.
“The final whistle needs to be blown on Thames Water, and (Prime Minister Andy) Burnham needs to get a grip.”
A straw poll conducted at the entrance to the Labour Party conference in Liverpool on Monday saw 99 of 100 votes cast in favour of public ownership of Thames Water.
Sophie Conquest of campaign group We Own It, which staged an event outside the conference, said: “Hedge funds or households? The choice really is that simple.”
“This Government can choose to sell off one of our most vital resources to US billionaires, or they can take it into public hands and run it in the interests of households, workers and our environment.”
