The bacteria, which can cause Legionnaires' disease, was found at Hinckley Leisure Centre on Tuesday.
The centre was thoroughly cleaned and further samples sent away for analysis contained no evidence of the bacteria.
The centre re-opened on Thursday afternoon. A council spokesman said further tests will be carried out at the centre over the next few days.
Pete Cash, Head of Culture and Development at Hinckley and Bosworth Borough Council, said: "The council has followed national guidelines and sought advice from the Health Protection Agency in dealing with the incident.
"The safety of the public is the main priority and the public should have confidence that the council and Sport and Leisure Management (SLM) are fully managing the situation and now consider the centre to be safe for public use."
He added that the council and SLM, which runs the centre, would like to apologise for any inconvenience the closure may have caused.
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