Connecting a rainwater tank to the toilet
Tank water can flush a toilet and fill a washing machine, if a licensed plumber connects it properly.
Yes, you can run toilet flushing and laundry cold water from a rainwater tank. But the connection is licensed plumbing work, and it needs a pump, a mains back-up and clearly marked pipes. You choose the plan. A licensed plumber builds it.
What the connection involves
Tank water does not reach your toilet by gravity. A pump pushes it into a separate line that runs to the cisterns and the washing machine cold tap. That line has to stay apart from your mains supply at all times.
Most setups add an automatic switch-over. When the tank runs low, mains water tops up the system so the toilet still flushes. Without it, a dry spell leaves you with a toilet that does not work.
The parts you will see on the plan
| Part | What it does |
|---|---|
| Pump | Pushes tank water through the house line |
| Mains back-up | Tops up from mains when the tank runs low |
| Backflow protection | Stops tank water flowing back into the mains |
| Marked pipework | Shows the line carries non-drinking water |
The backflow protection matters most. Tank water must never be able to creep back into the mains that feeds your kitchen tap.
Pipes must be marked, and the water is not for drinking
Pipework carrying rainwater is usually marked in lilac, so nobody mistakes it for drinking water. Read what the lilac pipe colour means before you plan any runs.
Flushing and laundry are a long way from drinking. Even so, never assume tank water is clean enough to drink. See whether tank water is safe to drink.
Is it worth doing
It depends on your roof and your tank. A small tank on a small roof runs dry quickly, and the pump and back-up cost you more than the water saves. A large tank on a big roof earns its place much faster.
Check tank sizing first. Then look at tank pumps and how a tank is plumbed. If the numbers do not stack up, do nothing yet.
Before you ask for a quote: a planning checklist
A licensed plumber builds the connection, but you decide whether it is worth it. Settle these points first and the quote will make more sense.
- Roof and tank. Work out whether your roof can keep the tank filled. A small tank on a small roof runs dry quickly.
- Where the pipes will run. The tank line must stay apart from the mains at all times, so look at where a separate line could go.
- Which fixtures. List the toilets and the laundry cold tap you want on the line.
- The back-up plan. Ask how mains water tops up the system when the tank is low, so the toilet still flushes.
- Local rules. Ask your state or territory plumbing regulator about backflow protection and pipe marking.
- Upkeep. Decide who will service the pump and check the screens.
If the numbers do not stack up after this, do nothing yet.
Mistakes to avoid with tank water indoors
| Mistake | Why it matters | What to do instead |
|---|---|---|
| Tying tank water into the mains | Tank water could flow back into the drinking supply | Use a separate line with backflow protection, fitted by a licensed plumber |
| Skipping the mains back-up | The toilet stops working in a dry spell | Ask for an automatic switch-over |
| Leaving pipes unmarked | Someone may mistake the line for drinking water | Use marked pipework, usually lilac |
| Assuming the water is clean | Roof runoff and tanks carry things you cannot see | Treat it as non-drinking; see whether tank water is safe to drink |
| Doing it yourself | The connection is licensed work in every state and territory | Choose the plan, then hire the licence |
| Buying before you size the tank | The pump and back-up can cost more than the water saves | Check sizing against your roof first |
Frequently asked questions
Can I connect a rainwater tank to my toilet?
Yes, in most places. A licensed plumber has to do the connection, with a pump, mains back-up and backflow protection.
Why does a tank connection need a mains back-up?
Tank water runs out in dry spells. A mains top-up keeps the toilet flushing when the tank is low.
Can tank water be used in the washing machine?
Often the cold tap can be fed from the tank. The rules differ by state, so ask your regulator first.
Can I do the connection myself?
No. Connecting a tank to household plumbing is licensed work in every state and territory.
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)