Treating rainwater tank water
No single filter fixes everything. Work out what is wrong first, then pick the treatment.
Tank water treatment is a set of tools, not one product. Each one handles a different problem, so the right choice depends on what a laboratory test finds in your water. Buying a unit before testing is guesswork.
Start with the source of the problem
Most contamination in a tank comes from the roof and the inlet. Fix that first. Leaf screens, a first flush diverter and a clean tank do more than any gadget on the kitchen tap.
Treatment is the last line of defence. It does not replace a tidy catchment.
What the common treatments do
| Treatment | What it helps with | What it misses |
|---|---|---|
| Sediment filter | Grit, fine dirt, cloudy water | Bacteria, chemicals |
| Carbon filter | Taste and smell, some chemicals | Many germs, unless rated for them |
| UV unit | Bacteria and other germs, when the water is clear | Chemicals, and it fails if the water is cloudy |
| Chlorine dosing | Germs held in the tank | Needs correct dosing and the right product |
UV only works on clear water
A UV lamp is often sold as the answer. It is only effective if a sediment filter sits in front of it, because cloudy water shields germs from the light. The lamp also ages, so it needs replacing on the maker's schedule even if it still glows.
Test before you treat
A NATA accredited laboratory can tell you what is in the water. Without that, you do not know whether you need a filter, a UV unit or just a cleaner tank. Run the test, then choose the treatment to fit.
Treatment can also give a false sense of safety. A filter that is never maintained becomes a source of contamination itself. If the water is not safe to drink, no unit on the tap changes that without confirmation from a test.
Many households do well using tank water for the garden and the laundry, and mains water for drinking. That is a sensible answer. See whether tank water is safe to drink for the wider picture, and how to clean a tank for the sludge side.
The order to follow before you buy any treatment
Spending on a unit before fixing the source wastes money. Work through the steps in this order.
- Fix the roof and the inlet. Leaf screens, a first flush diverter and clear gutters do more than any gadget on the kitchen tap.
- Clean the tank if it needs it. Sludge on the floor affects the water. See how to clean a rainwater tank.
- Test the water. A NATA accredited laboratory tells you what is in it.
- Choose the treatment to match the result. A sediment filter, carbon filter, UV unit or chlorine dosing each handle a different problem.
- Plan the upkeep. A filter that is never maintained becomes a source of contamination.
- Retest after the change. The lab can tell you whether it worked.
Questions to ask a tank water treatment seller
Treatment is a sales pitch for many people. These questions cut through it.
- What problem does this fix? A good answer names a result from a laboratory test, not a general promise.
- What does it miss? No unit handles everything. A UV unit does not remove chemicals, and a sediment filter does not remove germs.
- Do I need a sediment filter in front? UV only works on clear water.
- When does the lamp or cartridge need replacing? Follow the maker's schedule, even if the lamp still glows.
- Who installs it? Connecting a unit to house plumbing is usually licensed work.
- Can the water then be called safe to drink? Only a laboratory result can confirm that.
A sensible option for many households is tank water for the garden and laundry, and mains water for drinking.
Frequently asked questions
What is the best way to treat tank water?
There is no single best option. A laboratory test shows what is in the water, and the treatment is chosen to match it. Fixing the roof and inlet comes first.
Does a UV light make tank water safe to drink?
Only against germs and only when the water is already clear, which usually needs a sediment filter in front. It does not remove chemicals. Test the water to be sure.
Can I put chlorine in my rainwater tank?
Dosing needs the right product and the right amount. Get advice from your state health department or a tank specialist before doing it.
Do I need a licensed plumber to install a water treatment unit?
Connecting a unit to the house plumbing is usually licensed work. Rules differ by state and territory, so check with your regulator.
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)