Queensland Building and Construction Commission commissioner Brett Bassett said the work of plumber Brett George Hogan posed "a potential threat to public health".

Up to 800 properties in the south-east could be affected and Mr Bassett said the QBCC was working to contact all residents and property owners who may be affected.

"Yesterday I instructed my officers to contact each of the residents or owners of the 796 properties involved," he said.

"QBCC will be making every effort to contact residents through phone, email and direct mail."

Mr Hogan had replaced hot water systems at 796 properties since 2012, in areas including Wide Bay, Logan, Bundaberg, the Fraser Coast, Sunshine Coast, Moreton Bay and Gympie.

The QBCC began investigating Mr Hogan in September 2016, following complaints from the Moreton Bay council. In a four-month investigation of 28 properties, they found he had used a soft lead solder product with a lead content above the amount allowed by the Australian Standards in eight properties.

"Our current investigation suggests that Mr Hogan may have bought a bulk order or this solder, and may possibly have been using it for sometime. Therefore the QBCC is continuing it's investigation of Mr Hogan's activities, across all of Mr Hogan's notified works," Mr Bassett said.

Queensland's chief health officer Sonya Bennett said the risk of exposure to the lead was low, but people with hot water systems where the solder may have been used should avoid using hot water from the system for cooking or drinking.

"The chances of any lead being present in the water in those hot water systems is low, but not nil, and so Queensland Health will be working with the QBCC with respect to testing the relevant hot water systems," Dr Bennett said.

"It's probably important to note that general public health advice is not to drink from hot water systems for a range of reasons, some of which is the temp allows microbes to grow and other factors so people should always directly drink from cold water systems."

Water is being tested at four of the eight properties found to have the soft-lead solder, with results expected by Friday.

"If there is any lead found in those water results then public health officers will be directly contacting the households where there is lead found in the water and assessing their health risk," Dr Bennett said.

Mr Bassett said the vast majority of Queensland's approximately 1650 plumbers "do the right thing".

"This is one instance of the use of a non-compliant product," he said.

"The focus for me right now is working with my colleagues at Queensland Health and other government agencies to work through this very quickly and in the most appropriate way, to give people who may have been affected by the use of this product some comfort as quickly as possible."

The QBCC took disciplinary action against Mr Hogan in February. His licence was suspended for 12 months and he was fined the maximum penalty of $7000. He has since sought an external review of that decision through the Queensland Civil and Administrative Tribunal.

All local government areas potentially affected have been contacted by the QBCC.

Those who thought they may have been affected by work done by Mr Hogan should call the QBCC on 139 333 to arrange a free inspection.