Non-potable water: what it means and where you meet it at home
Water that is fine for the garden can make you sick in a glass. Knowing which pipe carries which water is the whole game.
Non-potable water is water that has not been treated or approved for drinking. It can be perfectly good for flushing a toilet or watering a lawn. It is not safe to drink, cook with or brush your teeth with, and clear water can still carry microbes you cannot see.
The word covers a lot of ground. Rain from the roof, water from a bore or dam, greywater and recycled water from a treatment plant are all non-potable unless something proves otherwise.
Where do you find non-potable water at home?
| Source | Usually non-potable? | What to know |
|---|---|---|
| Rainwater tank | Treat it as non-potable until tested | See tank water and drinking |
| Bore water | Yes, until a laboratory says otherwise | Quality changes block to block, see bore water |
| Dam water | Yes | Surface water, open to animals and runoff, see dam water |
| Greywater | Yes | Laundry and shower waste, see greywater |
| Recycled water | Yes | Supplied through its own pipes, often coloured purple |
How can you tell which pipe is which?
In Australia, recycled water pipes and fittings are normally lilac or purple, and taps on them are marked as not drinking water. Mains drinking water pipes are not. Do not rely on colour alone, though. A pipe buried in the yard or hidden in a wall tells you nothing, and old work may not follow today's rules.
If you are not sure, treat the tap as non-potable. A wrong guess in that direction costs you a trip to another tap.
Cross-connection is the real danger
The serious risk is not someone drinking from a sign-posted garden tap. It is a join between a non-potable supply and the drinking water pipes. Water can then flow backwards or mix without anyone noticing. That is why plumbing rules keep the two systems physically apart. And why a tank pump or bore line is never tied into the house mains on a hunch.
Backflow prevention devices exist to stop this. Fitting or testing them is work for a licensed plumber.
Non-potable does not mean dangerous for everything
Many homes use non-potable water for toilets, the laundry and the garden, and that is a sensible way to save mains water. The point is to match the water to the job. Do not fill a pet bowl, a kettle or a child's paddling pool from a tap you have not identified.
Can you make it drinkable yourself?
No, not in a way you can trust from the kitchen. A filter changes what is in the water, but it does not prove the result is safe. Only an accredited (NATA) laboratory can tell you what is actually in a sample, and your state health authority sets the guidance that applies to you.
Household rules for handling non-potable water
The aim is to match each water to a job. These habits keep people safe.
- Label every non-drinking tap. A clear tag helps guests and children.
- If you are unsure, treat the tap as non-potable. A wrong guess in that direction costs you a trip to another tap.
- Keep hoses and bowls separate. Do not fill a pet bowl, a kettle or a paddling pool from a tap you have not identified.
- Never join systems. A tank pump or bore line is not tied into the house mains on a hunch.
- Test before you decide anything. Only an accredited (NATA) laboratory can tell you what is in a sample.
- Call a licensed plumber for any connection. Backflow prevention is licensed work.
Good uses for non-potable water at home
Non-potable does not mean useless. Many homes use it well.
| Use | Usually fine? | Note |
|---|---|---|
| Toilet flushing | Often yes | Needs a licensed connection and a mains back-up |
| Laundry cold tap | Often yes | Rules differ by state; ask your regulator |
| Garden watering | Yes | Salty or iron-heavy water can damage plants |
| Washing the car | Yes | Check for staining |
| Drinking and cooking | No | A filter does not prove the water is safe |
| Pet bowls, kettles, paddling pools | No | Use only a tap you have identified |
See what lilac pipe means if you meet coloured pipework.
Frequently asked questions
What does non-potable water mean?
It means water that has not been treated or approved for drinking. It may suit toilets, laundry or the garden, but it is not safe to drink or cook with.
Is rainwater potable?
Not by default. Tank water should be treated as non-potable until an accredited NATA laboratory has tested it and your state health guidance says it is suitable.
What colour are recycled water pipes in Australia?
Recycled water pipes and fittings are normally lilac or purple. Do not depend on colour alone, because older or buried pipework may not be marked.
Can I connect a non-potable supply to my house plumbing?
Not on your own. Connecting a tank, bore or recycled supply to the house needs a licensed plumber and the right backflow protection, under your state or territory rules.
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
- Sydney Water. Water supply, wastewater and stormwater services