The big water tank which has been key to providing Katherine with PFAS-free drinking water is being temporarily taken out of service at the end of the year.
Power and Water's nine million litre tank needs a new $2 million roof.
The upgrade comes as the town prepares for its new water treatment plant designed to clean PFAS contamination from all of the town's supplies.
Commissioning of the new plant has now been delayed until next year.
The nine megalitre tank is not the biggest at the Morris Road water works, a 12 megalitre tank is used to supply the Tindal RAAF Base, where the chemical contamination leaks from.
The 40-year-old roof on the town's tank is corroded and "has reached the end of its life".
This tank is currently used to store treated water to service the town and will continue to be used after the re-roofing works.
At crucial times, mostly at the end of the dry season when Katherine River supplies cannot be relied on and the contaminated bores are in use, treated water is stored there to keep drinking water supplies flowing.
Officials rely on town-wide water restrictions and as much "safe" water as they can squeeze into the big tank to guarantee PFAS free water.
Katherine generally uses the entire contents of the big tank each day.
The tank will be taken out of service during the wet season from January to April 2021 which is when demand on the town's water supply is the lowest.
While the nine megalitre tank is out of service, a 4.5 megalitre tank will store treated water to service the town.
"If this is insufficient to meet demand, we will bring on the 12 megalitre tank which services Tindal to meet Katherine's additional needs," a Power and Water spokeswoman said.
"We will clean and refill the tank when roofing works are completed. We will also test the water to ensure it meets all health requirements before we return the tank to service."
The major objectives of the project are:
- Complete re-roof of the existing ground level water tank
- Removal of the existing roof beams for re-galvanising off-site - then reinstatement of beams
- Modify roof perimeter handrail system to comply with Australian Standards
- Removal and reinstatement of roof furniture including access hatches and roof ventilation
- Supply and install new internal and external stair system
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