Redbridge Town Hall suffered water damage after a leak from a disused pipe on Friday.
Ceilings and floors on the third floor of the Grade II listed building in High Road, Ilford, were damaged after the redundant pipe was not capped off correctly, according to a council spokesman.
That led to a full flow of water through the system when a fault was being tested.
The spokesman said a valve was then found to stop the flow.
The council has not said how long the leak lasted for.
Cllr Ian Bond, a Liberal Democrat councillor for Roding ward, tweeted on Friday: “Town Hall offices slowly filling with water as LBR [London Borough of Redbridge] system springs a leak.”
He later tweeted: “Water Board reconnected ancient disused mains pipe by mistake.
“Another crisis quickly resolved thanks to excellent Redbridge staff.”
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here