Merton High Street had to be closed after the pipe burst. Pic by Kati Sarab
About 15,000 properties in south London were left without water for about seven hours on what was one of the hottest days of the year.
Thames Water said a major water main burst on Merton High Street in south-west London on Sunday morning, cutting supplies to customers.
Engineers managed to fix the leak and supplies were back on by mid-afternoon.
Some shops had to ration bottled water after people rushed for supplies as temperatures rose to about 30C (86F).
Kingston, Merton, Wimbledon and Surbiton were among the affected areas.
Tesco in Kingston brought in rations of 12 two-litre bottles or three five-litre bottles of water per customer.
Bart Ricketts, a borough councillor in Kingston, said: "Sainsbury's in Surbiton was nearly sold out of water when I went there at 2pm.
"Families needed water even more in the hot weather but fortunately it wasn't off for too long."
A spokesman for Thames Water had earlier apologised for the inconvenience and said people with special needs, such as those with young children or people looking after the sick or elderly, could call the company's customer services for advice.
Thomas Hoskins, who lives in Wimbledon, south-west London, earlier told BBC London the problem was an "absolute disaster on a day like this".
Chris Gleeson from Raynes Park said: "I just went to the bathroom and turned on the tap to find no water, so I haven't been able to have a shower or flush the toilet.
"We do have bottled water so we've had a cup of tea this morning but it is causing real problems."
The incident also caused travel disruption with Merton High Street closed in both directions while the burst main was repaired.
South Wimbledon Station was shut due to flooding but later reopened.