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Septic tanks and flooding

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Septic tanks and flooding: What you need to know about your septic tank after a flood.

View the full PDF resource from Te Whatu Ora here


What’s the risk?

During a flood event, septic tanks and the drainage area may become flooded. This can clog up pipes which may cause a sewage backup (smelly black liquid) in toilets/drains. Other signs your septic tank may be affected include slow draining toilets and drains, and a smell of sewage.

If you’re a septic tank owner and experience any of the above, you will need to arrange temporary toilet facilities. Please refer to our factsheet on sewage disposal for temporary toilet options.

Septic tanks: What to do?

• Check gully traps for debris and silt and remove material so that it is not flushed into the tank.

• Check outlet filters on the septic tank for clogging and clean or replace if necessary. Flooding of the tank will lift scum and fats that may block the outlet or outlet filter.

• Ensure stock cannot access the drainage field area.

• Reduce water usage in your home until the septic tank system restores itself and the water table falls.

If you have concerns that the system has become damaged or clogged with silt or debris, we recommend that you have your septic tank and drainage field professionally checked and cleaned.

Refer to the Yellow Pages to locate septic tank contractors.


⊗ use your septic tank system until the floodwaters over the
drainage field have gone

⊗ pump out your septic tank during flood conditions or
saturated soil conditions as it may cause the tank to rise out
of the ground, damaging the pipework

⊗ attempt to clean out the septic tank yourself — tanks may
contain dangerous gases (use the Yellow Pages to locate
septic tank contractors)

⊗ drive or operate heavy machinery over the drainage field
as saturated soil is easily compacted — this will reduce the
ability of the soil to absorb wastewater

⊗ drink water from bores/wells close to flooded septic tank
systems until the water has been tested and found to be safe.

Important health tips

Wash and dry your hands, every time, after using the toilet, handling human waste or checking your septic tank system.

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