London Fire Brigade had to declare a major incident due to its call centre being inundated with emergency calls during July's floods, it has emerged.
Parts of London received a month's worth of rain in just one day on 12 July, causing flash floods.
The brigade reported its highest number of calls on record and scrambled to bring in extra staff, City Hall heard.
The head of London Resilience said agencies would now prepare for potential floods earlier in future.
The fire service was among the agencies updating City Hall's fire, resilience and emergency planning committee three months on.
The committee was told 1,430 calls had been made to the brigade control centre at the peak of the flooding between 17:00 BST and 21:00, with 3,000 in total over that 24-hour period.
David O'Neill, the brigade's deputy assistant commissioner, said the public reaction to the emergency left the service's ability "compromised".
He said: "It was declared a major incident and that was because special arrangements had to be put in place, and that was the recall of staff and the diverting of calls to other call centres around the country.
"That's a way for us to alert partners to the fact that the London Fire Brigade response has in some way been compromised."
As a result, the head of London Resilience, John Hetherington, said agencies would now start preparing for potential floods when there were yellow weather warnings, rather than amber as before.
He said it was clear communication with the public and the co-ordination of the flooding response could be improved, but added "we should not be preparing and putting all our eggs in the response".