Cleaning rainwater tanks impacted by floodwater

Rainwater tanks impacted by floodwater are likely to contain harmful organisms, and the water in affected tanks is not suitable for drinking.

Cleaning rainwater tanks

Tanks that have been completely submerged and have large amounts of floodwater inside need to be drained and cleaned to remove most of the contaminated water and sludge. This includes rainwater tanks whose entry points have been submerged.

When draining and cleaning the tank, make sure you are not alone and avoid entering the tank. Sludge on the bottom of the tank should be removed as part of the draining process.

If you have a pump and hose, use them to remove the water and sludge. If you have a second source of water, such as mains water, use this to hose down the sides and bottom of the tank. Remove any small animals or birds that may be in the tank, using a net or other tool.

Avoid scrubbing the inner surfaces of tanks as it can destroy protective layers.

Disinfecting drinking water in rainwater tanks

If you are concerned your tank water may have been contaminated, it should be disinfected before drinking.

You can disinfect the rainwater by mixing chlorine in a bucket or two of water before adding to the tank. Always follow the warnings, directions for use and safety precaution advice on the product label. As a guide, chlorine may be diluted as follows:

  • liquid swimming pool chlorine (12.5% concentration): 40mL or 40g of chlorine to 1000L of water
  • granular swimming pool chlorine (70% concentration): 7g of chlorine to 1000L of water

After you add the chlorine, allow the water to stand for at least one hour before drinking (or overnight if possible).