Schools were forced to shut due to the incident on Wednesday morning, with the water firm saying the issue at its Ashford and Hampton treatment works had impacted more than 50 postcodes.
The firm’s interim joint chief executive, Cathryn Ross, told an afternoon meeting of the London Assembly’s environment committee that it will investigate the problem’s cause and the effectiveness of Thames Water’s response.
The committee’s Labour chair, Leonie Cooper, asked Ms Ross “how on earth” the incident had happened, adding that it was “not a great look” for the company.
After apologising for the disruption, Ms Ross said: “We will do a review. We will look at what the root cause was, we’ll look at whether there was anything we could have done better, and we’ll obviously learn lessons.”
She said that as far as the company was aware at this stage, the issue was caused by a power outage, rather than a fault of Thames Water’s own equipment.
“Within an hour of the original outage, we had begun to restore flow,” she said.
The company has put three bottled water stations in place at key locations in the affected area, she said, adding that they will remain in place for as long as they are needed.
Two hospitals - the Royal Hospital for Neuro-disability in Putney and the West Middlesex University Hospital in Isleworth - were affected. Ms Ross said that Thames Water offered to provide them both with a tanker supply, but both were back on normal supply before that was necessary.
The Shooting Star Children’s Hospice in Hampton was also affected and offered support, but already had its own water on supply, Ms Ross said.
The following postcodes were hit by the problems: SW4, SW8, SW9, SW13, SW14, SW15, SW18, SW19, TW1, TW2, TW3, TW4, TW5, TW7, TW8, TW9, TW10, TW11, TW12, TW13, TW14, TW17, W1H, W1H, W1M, W1N, W2, W3, W4, W6, W7, W10, W12, W13, W14.