Waltham Forest Council has moved to downplay an investigation into potential Legionella at its buildings, insisting school children are not at risk.
The Health and Safety Executive (HSE) has launched a probe into the authority amid concerns people may have been put at risk of developing Legionnaires' disease, which can kill in some cases.
A council spokesman described the probe as "low key" and said the authority had started routine work to address the issue at sites last week.
The works had previously been recommended by the HSE.
The Guardian understands that the probe centres around claims that the authority has not been properly managing water systems safely in order to prevent the spread of the Legionella bacteria.
It can grow to dangerous quantities in water in heating systems and other plumbing under the right conditions and temperatures.
People can then catch Legionnaires' disease by inhaling the bacteria from droplets in the air.
A recent outbreak of the pneumonia-type illness from a cooling tower in Edinburgh last summer killed two people and hospitalised dozens.
An NHS spokeswoman told the Guardian it was not aware of any cases of Legionnaires' disease in Waltham Forest.
The Guardian understands that one major site being investigated by the HSE is George Mitchell School in Leyton.
A council spokesman said: "There is no outbreak or risk of Legionella at George Mitchell School.
"Regular risk assessments take place on all school and council buildings to ensure their safety and we carry out recommended maintenance work accordingly.
"The HSE have confirmed that the nature of their investigation is ‘low key’ and to do with procedural matters.
"The HSE is seeking reassurances that we have addressed the recommendations made, which were to carry out routine maintenance and cleaning works to water facilities.
"This work started last week in half term and is due to be completed this week."
He added: “We have been in touch with the HSE and updated them on the planned maintenance work which took place during half term and will update them again when the works are completed later this week.”
It comes just months after the HSE started a separate investigation into alleged council failures to manage asbestos in its buildings.
The HSE launched the investigation into the toxic fibre at Waltham Forest Town Hall in August 2011.
The probe was then widened to include an asbestos find at the former Warwick School for Boys site in Brooke Road, Walthamstow.
The HSE is now investigating the council's asbestos management at all its buildings.
Three classes and 18 staff at St Mary's Church of England Primary in The Drive, Walthamstow, moved to the Brooke Road building in September 2011, before asbestos was discovered there during the summer holidays.
The entire school had been due to relocate there in September 2012 but that was postponed following the discovery.
In November the council reportedly told parents it would launch its own investigation to see if any children had been put at risk of the asbestos, but had previously denied this was the case.