Safety and first aid

Wastewater after cyclones, floods and other disasters

Septic tanks 

Flood waters may affect your septic tank system, which is also known as an onsite wastewater system.

How will I know if my septic tank system has been affected?

Septic tank systems typically comprise a concrete, plastic or fibreglass tank.

The tank collects wastewater from:

  • toilets
  • bathroom
  • kitchen
  • laundry.

Most septic tanks should not be structurally damaged by flooding as they are below ground.

However, flood water may enter your septic tank system through the toilet, other fixtures or the overflow relief gully grate.

Flooding of the septic system may wash out solids from the tank causing blockages or system damage.

Safety issues that need to be checked:

  • open covers/pits
  • ruptured/leaking systems (including pipes)
  • damaged/exposed pipes that may need capping/sealing off.

Failed systems are not easy to identify. However, some simple indicators may include:

  • a pungent odour around the tank and land application area
  • blocked fixtures, with wastewater overflowing from the relief point
  • high sludge levels within the primary tank
  • sewage flowing up through the toilet and sinks.

Some onsite wastewater treatment systems may rely on mechanical and electrical equipment, such as pumps, aerators and filters.

This equipment may be damaged by flood or loss of power.

To prevent injury or further damage to your system contact your service agent.

What can happen to the septic tank during a flood?

Flooding of the chambers in the septic tank or primary/secondary treatment tanks can lift the floating crust. This naturally forms on top of the wastewater and includes:

  • fats
  • grease
  • other materials.

If the tank becomes flooded, the crust can lift and then block either the inlet or outlet of the septic tank pipes.

This may cause solids to transfer from the septic tank to the leach drain or disposal system.

In addition, septic tanks, leach drains, pump pits and irrigation pipework can fill with silt and debris.

This will either reduce the capacity or the effectiveness of the treatment system.

What should I do if my septic tank has been under flood water?

Do not use any toilets, laundry, kitchen, bathroom or clean-up equipment connected to the onsite wastewater disposal system until:

  • all parts of the wastewater treatment and disposal system have been professionally inspected and repaired
  • your onsite wastewater disposal system has been approved for use by the local authority environmental health officer.

Contact your local authority environmental health officer for more information.

How can my septic tank be repaired?

a collapsed septic tankOnly trained specialists are suitably equipped to clean or repair onsite waste disposal systems.

This is because tanks may contain dangerous gases and other harmful materials.

Contact your local authority environmental health officer for a list of wastewater disposal system contractors who work in your area.

Onsite wastewater disposal systems should be pumped out by a licensed septic tank operator as soon as possible after the flood.

However, it is important to ensure that the water level in the ground surrounding the tanks is as low as possible before you start.

It is possible for empty tanks to float out of the ground causing damage to underground pipework.

Aerated wastewater treatment system

Aerated wastewater treatment systems (AWTS) should not be used if it has been inundated with floodwater.

Isolate the electrical connection and call the service technician immediately.

Sewage overflows

In all situations where a sewage overflow (also referred to as wastewater overflow) clean up procedure is needed for your property, persons involved in the clean-up procedure should wear personal protective clothing such as rubber boots, rubber gloves and washable or disposable coveralls.

Unprotected persons should be evacuated from the affected area until the area has been thoroughly cleaned and disinfected.

Other safety precautions to be followed include:

  • Assume anything touched by wastewater is contaminated.
  • Wash your hands and affected areas of the body thoroughly with clean warm water and soap, especially before eating or smoking.
  • Immediately wash and disinfect any wounds that come into contact with wastewater.
  • Change out of dirty clothes and wash clothes separately.
  • Clean and dry dirty footwear.
  • Contact your doctor immediately if you experience any illness.

Read more about domestic wastewater overflows.

More information


Acknowledgements
Public Health

This publication is provided for education and information purposes only. It is not a substitute for professional medical care. Information about a therapy, service, product or treatment does not imply endorsement and is not intended to replace advice from your healthcare professional. Readers should note that over time currency and completeness of the information may change. All users should seek advice from a qualified healthcare professional for a diagnosis and answers to their medical questions.

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