Restoring rainwater tanks affected by natural disasters (including bore water-holding tanks)
Rainwater tanks and bore water-holding tanks impacted by storms, floods, bushfires and other natural disasters are likely to contain harmful organisms. This is likely to mean the water stored in the affected tanks will not be suitable for normal use.
What to consider when restoring tanks
It is important to first assess the structure of your tank and the surrounding environment to ensure it is safe to begin restoration works. If damaged or relocated, tanks have the potential to pose a drowning hazard and access should be appropriately restricted.
If you know or suspect that electrical equipment associated with your tank has been affected, it is recommended that it is inspected and declared fit for use by a licensed electrician before attempting to restore the tank.
Under Queensland legislation, all water storage tanks must have at every opening of the tank:
- mosquito-proof screens that:
- are made of brass, copper, aluminium or stainless steel gauze
- have a mesh size of not more than 1mm
- are installed in a way that does not cause or accelerate corrosion
- stop mosquitoes passing through the openings
- or flap valves that, when closed, stop mosquitoes passing through the openings.
Rainwater tanks and bore water-holding tanks that have been damaged or are missing screens or flap valves as a result of storms and floods may provide ideal breeding sites for mosquitoes capable of carrying diseases. Action should be taken, as soon as is safe to do so, to ensure mosquitoes are prevented from breeding in these tanks. Read controlling mosquito breeding after floods for more information.
Reinstating the rainwater or bore water-holding tank
If your tank has been inundated with flood waters, the water will have been contaminated and should be discarded. If you have an underground tank, you should not attempt to empty it while the surrounding ground is still saturated. Emptying water before the surrounding ground has dried out may result in damage to the tank and associated plumbing.
Once the tank has been emptied, the inside of the tank should be hosed out with clean water and sanitised. Any associated plumbing, guttering, downpipes and roof surfaces inundated by flood waters will also need to be cleaned and sanitised. A rainwater and bore water holding-tank supplier will be able to advise on the best sanitation method depending upon the material the tank is constructed of. If cleaning of the tank requires entering the tank, it is recommended that a qualified, professional tank cleaner undertake this activity as working in a confined space is hazardous.
Cleaning agents that release hazardous fumes or adversely affect the water quality after cleaning should not be used.
After cleaning and sanitisation has taken place, the tank should be refilled with water from a source known to be safe and should be appropriately disinfected using enough chlorine to give an initial chlorine dose of 5mg/L. The amount required will depend on what form of chorine you use and how much water is in the tank. However, as a general rule:
- household bleach (4 percent concentration)—125 ml or 125g / 1000 litres
- liquid swimming pool chlorine (12.5 percent concentration)—40 ml or 40g/1000 litres
- granular swimming pool chlorine (70 percent concentration)—7ml or 7g/1000 litres.
When using chlorine it is important to remember to adhere to the warnings, directions for use and safety precaution advice contained on the product label.
After adding, allow to stand for at least one hour (or overnight if possible). You will need to calculate the amount of water in your tank to determine the appropriate amount of chlorine to put in. The Australian Government's Department of Health website provides guidance on the use of rainwater tanks, including how to calculate the volume of your tank and chlorine dosing.
- call 13 QGOV (13 74 68) or contact your nearest Queensland Health public health unit
- visit the Get Ready Queensland website
- contact your local council.