Cairns health officials warned that elderly people and children were most at risk and advised residents to either boil water or buy bottled water until further notice. 

Queensland Health water scientists and medical officers said poorly maintained reservoirs were exposed to potential contaminants from cockroaches, vermin, bird faeces, lizards and frogs.

"The Public Health Act requires water service providers to supply safe drinking water and we have a duty of care to our community," Cairns Regional Council general manager of w ater and waste Bruce Gardiner said. 

"Queensland Health has advised that as a precaution, residents in Port Douglas, Craiglee, Mowbray, Rock Point and Daintree Village should boil all drinking water until further notice."

Chair of the council's Water and Waste Committee Cr Paul Gregory said the water supply would be given a one-off dose of chlorine to kill the bacteria, and an audit and restoration program of the reservoirs would cost a "significant amount" and take up to 12 months to complete.