The company said it promised to investigate how the main came to collapse and what it can do to avoid it happening again.
A spokesman said its "options were limited for a failure of that size".
The burst happened in the early hours of Wednesday near a pumping station at Willsbridge, between Bristol and Bath.
It led to many schools and businesses having to close for the day with shops soon selling out of bottled water. The service has now been fully restored.
Water bowsers were eventually sent to three locations around Keynsham but there was criticism they were not in other places affected by the outage.
More on this and other stories from the Bristol area.
Ben Newby from Bristol Water said the fault had happened on a "strategic main".
"It's the size of the failure and the amount of people impacted and has been one of the biggest incidents in our history," he said.
"Our priority is always on isolating it [the burst], getting people back on supply, putting a permanent repair in place and then analysing the way the main collapsed or fractured - and what can be done to stop it happening again."
"Next we reconfigure the network to re-supply people. You inevitably get some air in the supply... so it's likely people get some discolouration or murky water.
"But if you run the taps for a while it soon clears."
A water main burst which affected some 35,000 homes and businesses has been described as one of the "biggest incidents" in Bristol Water's history.