Schools and libraries closed on Monday and there was widespread traffic disruption after a burst water main flooded part of Kennington Park Road.
According to Thames Water, homes and businesses in SE1, SE5, SE11, SE17, SE24 and SW9 had their water supply disrupted by the burst water main.
The burst water main was on the Lambeth/Southwark border at Kennington Park Road and had a major impact on both boroughs.
"A 20 inch water main burst and surface water flooded 200 metres of Kennington Park Road to half a metre deep," said London Fire Brigade's Star Gareth Cook.
"Fire crews carried out pumping operations, placed sand bags by affected properties and used booms to guide floodwater down drains. Around 15 properties were flooded along Kennington Park Road."
When the flood was at its height, 10 fire engines and 72 firefighters and officers from Lambeth, Brixton, Clapham, Homerton, Old Kent Road, Dowgate, Dockhead, Tottenham and West Hampstead fire stations attended the incident.
"We are aware of the burst Thames Water main in Kennington that has been affecting the water supply in large parts of Southwark and Lambeth," said Cllr Darren Merrill, Southwark's cabinet member for environment and public realm.
"Thames Water is the lead authority and is working to fix the pipe. We have been informed that they have now isolated the problem and residents should begin to see water supply return gradually.
"We are not currently aware of any homes in Southwark that have been flooded due to this morning's incident, and our main priority is still identifying and assisting any vulnerable residents who may still be experiencing difficulties while full repairs are carried out and water is restored.
"Two libraries and nine schools in Southwark have closed. We know what an inconvenience this is for many people, especially in this hot weather, and Thames Water has assured us they are doing all they can to fix the pipe."
Traffic at Elephant & Castle – already affected by roadworks – was further disrupted by the road closures caused by the flood.