A dead animal in your water tank
Stop using the water first. Everything else can wait ten minutes.
If an animal has died in your tank, stop using the water for anything you or your pets drink, cook with or wash with. And do not drain it in a hurry. The water is contaminated until the animal is out, the tank is cleaned and the water has been tested.
First, confirm what you are dealing with
A bad smell, a sour taste or cloudy water can be the first sign. Look through the inlet or inspection hatch with a torch, from a safe position. Do not climb in and do not lean over an open tank.
Small animals get in through a damaged screen, a gap at the inlet or an open overflow pipe. Frogs, possums, rats, birds and lizards are the usual ones. Finding the entry point matters as much as removing the body.
What the contamination means
A dead animal can add bacteria and decay products to the water. Boiling does not remove everything that matters. Treat the whole tank as non-drinking water until it has been cleaned and tested.
- Stop drinking and cooking with it. Switch to mains or bottled water.
- Keep children and pets away from the tank water.
- Switch off the pump if the tank feeds the house, so the water does not spread through the pipes.
- Leave the water alone until you have a plan for removing the animal and cleaning the tank.
Removing it and cleaning up
Wear gloves and eye protection, and wash well afterwards. Take the animal out with a net or a long-handled tool, bag it and bin it. If you cannot reach it safely, call a tank cleaning service.
After the animal is out, the tank needs a full clean, not a quick flush. Sludge on the floor holds most of the contamination. See how to clean a water tank for the steps, and treating tank water for what disinfection can and cannot do.
| Situation | What to do |
|---|---|
| Small animal, tank used for garden only | Remove it, clean the tank, fix the entry point |
| Tank feeds toilets or laundry | Switch to mains, clean the tank, flush the lines |
| Anyone drinks the water | Stop drinking it, clean the tank, test at an accredited lab |
| Animal too large or out of reach | Call a tank cleaner |
Why you should not drain it in a hurry
It is tempting to pull the plug and start again. Think first. A full tank is a lot of water, and draining it onto a slope can cause erosion or send contaminated water toward a neighbour. Check where the outlet will discharge before you open anything.
If the tank is steel or concrete, a sudden empty can also stress the walls. Poly tanks cope better, but a tank that is nearly empty can float or shift in a high water table. Draining slowly, with the animal removed first, is the safer order.
What the sludge tells you
Rainwater tanks collect fine sediment on the floor over the years. A dead animal sinks into that layer and breaks down there. That is why a quick rinse rarely works: the smell comes back because the sludge was never removed.
A proper clean means getting that layer out. A tank cleaning service uses a vacuum system that does it without draining the whole tank. For a small tank, you may prefer to pay for this rather than do it yourself. It is not worth risking a confined space for a job a contractor does in an hour.
Do not skip the plumbing
If the tank feeds a pump, a toilet, a laundry or a hot water system, the contaminated water has already travelled into the pipes. Once the tank is clean and refilled, run the taps for a few minutes to push the old water out. Do the same at the toilet and the washing machine inlet.
If your hot water system draws from the tank, tell your plumber. Do not go looking inside the unit yourself. That part is not yours to touch.
Test before you drink again
Clear water does not mean safe water. Rainwater, bore or tank water for drinking should be tested by a NATA-accredited laboratory. Ask your state or territory health department what applies to you. Read is tank water safe to drink first.
Stop it happening again
Fit fine mesh over the inlet and the overflow, and keep the hatch closed. Check the screens each season and after storms. Trim branches that give animals a bridge onto the roof.
Frequently asked questions
Is tank water safe after a dead animal was in it?
Not until the animal is removed, the tank is cleaned and the water has been tested by an accredited laboratory. Until then, treat it as non-drinking.
Can I just boil the water?
Boiling is not a reliable fix for a contaminated tank. Remove the cause, clean the tank and test the water.
How do I know there is an animal in my tank?
A bad smell, a sour taste or cloudy water are common signs. Check through the inspection hatch with a torch from a safe position.
How do animals get into a tank?
Usually through a damaged inlet screen, a gap around the hatch or an unscreened overflow pipe. Fine mesh and a closed hatch stop most of them.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- NHMRC. Australian Drinking Water Guidelines
- Australian Building Codes Board. National Construction Code — Volume Three (Plumbing Code of Australia)