How to Sterilise Your Water Supply Tanks

The Council recommends you sterilise your tank annually. Ideally tank cleaning should be carried out by tank cleaning contractors. A Google search should direct you to tank cleaning providers in your area.

WARNING: If you enter the tank to clean it, please ensure there is adequate ventilation and another person is present.

If the tank has no accumulated material in it, steps 2-4 below may be omitted.

1. Turn off the water supply into the tank.
2. Drain the tank completely.
3. Clean out the inside of the tank of all accumulated matter.
4. Liberally spray chlorine based bleach product over the internal floor and walls of the tank.
5. Check strength of chlorine in bleach. Quantity below assumes 4% sodium hypo chloride. Refill the tank adding 0.3 litres of chlorine bleach per 1000 litres (220 imperial gallons) of tank volume.
6. Allow this water to stand in the tank for at least 30 minutes.
7. Drain the tank completely flushing with clean water.
8. Refill the tank with fresh water.

The use of chlorine bleach in steps 4 and 5 will ensure that the tank is adequately sterilised and suitable for holding drinking water. It is important that the tank is completely drained at step 6 as the strong chlorine concentration will make the water extremely unpleasant to drink.

For more information on water collection tanks and safe household water, please refer to this Ministry of Health factsheet.

Please exercise due care in using ladders to gain access to the tank, as these can be treacherous when wet.

Remember, you plan to drink the water at the completion of the cleaning so be very careful with the cleanliness of all items entering the tank.

Should you be on a Restrictor System you need to be aware that the filling time for your tank will be extended.

If you require assistance calculating the volume of the tank please measure the diameter and water depth of the tank then phone the Council on 687 7200.