Authorities warned people in part of Bullsbrook in the City of Swan, about 35km from the Western Australia capital, that they could be at risk and a hazardous and toxic materials (HAZMAT) alert has been issued.

“During bushfire suppression operations to protect the Bullsbrook College and surrounding properties (on Wednesday, helicopters) drew from water sources that have been identified as sewerage wastewater holding ponds,” the Department of Fire and Emergency Services said on Thursday. Authorities urged residents not to be alarmed and said the forecast high temperatures in the area into the weekend would help neutralise any residual bacteria contained in the effluent.

The temperature in Perth on Thursday is forecast to reach 39C, followed by 41C on Friday and Saturday, with 38C expected on Sunday.

“No buildings were directly targeted during bushfire suppression activities but properties surrounding the bushfire area may have been impacted by some aircraft drift spray,” the HAZMAT alert said.

The bushfire, which has threatened lives and homes near Royal Australian Air Force base Pearce, continues to burn but it has been contained and controlled.

It reached an emergency-level warning on Wednesday and burned through nine hectares of properties and bushland before firefighters and water-bombing aircraft got the upper hand.

The Department of Defence confirmed the ponds the sewage wastewater was drawn from are fed from reticulated water supply and do not have any PFAS chemicals present.

Residents in the impacted area who have water tanks for household use have been urged to empty their tanks and hose down structures and vehicles if they have been contaminated.

“Maintain personal hygiene as a high priority,” emergency services said.

People with vegetable gardens or fruit trees have been told not to harvest crops for two days and thoroughly wash any produce before consumption after this period.