Use tap water treated with a conditioner that names chloramine on the label, matched to the tank’s temperature. Rainwater, bore water and pure RO or distilled water all need testing or extra treatment, and leaving tap water to stand does not remove chloramine.
If you’re wondering what water to use for fish tank set-ups, the answer for most Australian homes is plain tap water with a water conditioner. Tap water is consistent, carries the minerals fish need and is easy to treat. The conditioner has to handle chloramine as well as chlorine, because many Australian supplies use it. Other sources can work, but each has a catch.
This guide sits in our Testing & Treatment guides. For the routine itself, see how to change fish tank water.
What Water to Use for Fish Tank Set-Ups: Every Option Compared
| Water | Use it? | The catch |
|---|---|---|
| Tap water plus conditioner | Yes, the default | Needs a conditioner that removes chloramine as well as chlorine |
| Tap water left to stand | Only if your supply is chlorine-only | Standing does not remove chloramine |
| Rainwater | Sometimes, after testing | Slightly acidic, almost no minerals, can carry zinc or roof debris |
| Bore water | Only after a lab test | Can be salty, iron-rich or high in nitrate |
| Bottled spring water | Rarely worth it | Mineral content varies by brand and batch; mineral water is often too hard |
| Distilled or RO water | Mixed or remineralised only | No minerals or buffer, so pH can swing |
| Softened water (salt softener) | No | Swaps calcium for sodium |
| Hot tap water | No | Can carry metals from the hot water system and pipes |
Tap Water: Why It Wins, and What Chloramine Changes
Tap water is the best starting point because it’s safe, steady from week to week and already carries calcium and other minerals that buffer pH. What makes it unsafe for fish is the disinfectant. Chlorine breaks down and escapes if water stands. Chloramine, a longer-lasting mix of chlorine and ammonia, doesn’t, and it is toxic to fish.
Sydney Water says it adds chlorine and ammonia to drinking water, and that these can affect fish. It suggests either standing the water for 48 hours to dechlorinate it, or an aquarium conditioner that removes chlorine and chloramine. Only the conditioner deals with chloramine. Treatment differs by city and even by suburb, so unless your water authority confirms chlorine only, treat every bucket as if it carries chloramine.
Chloramine also releases a little ammonia when it is broken down. A healthy, cycled filter handles it, and many conditioners bind it too. Our roundup of water conditioners compares the options.
Can You Use Rainwater in a Fish Tank?
Sometimes, with care. The Australian Government’s enHealth guidance on rainwater tanks says tank rainwater tends to be slightly acidic. It adds that new galvanised tanks can leach excess zinc, and new concrete tanks can push pH up. Acidic run-off can also pick up lead from old roof flashing.
Those are small numbers for people but not for fish. ANZECC’s freshwater guidelines set a trigger value of just 8 micrograms of zinc per litre to protect aquatic life. Rainwater also has almost no minerals, so pH can crash without buffer. If you use it, test pH, KH and GH first, and mix it with tap water rather than using it straight. Our KH and GH explainer covers what those numbers mean.
Bore Water, Bottled Water and RO Water
Bore water is a gamble until it’s tested. HealthyWA advises a lab test by an accredited laboratory before bore water is used for anything beyond the garden. Common problems include salinity, iron and nitrate, and all three matter in a tank. Nitrate in particular adds to what your fish already make, as our nitrate vs nitrite explainer explains.
Bottled spring water is safe but pointless for most tanks. The mineral content changes by brand and batch, so it’s harder to keep stable than tap water. Carbonated or mineral water is out.
Distilled and RO (reverse osmosis) water are almost pure, which sounds ideal but isn’t on its own. With no minerals or buffer, pH can swing wildly. Keepers use RO for soft-water specialists such as discus and some shrimp, or to dilute very hard tap water, then add a remineraliser or blend it with tap water to a target hardness.
Matching the Water to Your Fish
Water type matters less than the numbers in it. Most community fish do well in pH 6.5 to 7.5, and goldfish do best around 6.8 to 7.4. Australian tap water varies a lot: Sydney Water lists its supply at about 57 mg/L as calcium carbonate, which counts as soft, while some inland and western supplies run much harder. Test your tap water before you buy fish, and choose fish that suit it. Our guide to what pH a fish tank should be has the ranges by fish group.
Whatever the source, match the temperature to within a degree or two of the tank before it goes in.
Frequently Asked Questions
Can I use tap water for my fish tank?
Yes, once it’s treated. Add a conditioner that removes chlorine and chloramine, match the temperature, and the water is ready.
How long do you let tap water sit before adding fish?
About 48 hours removes chlorine, but standing does nothing for chloramine. Because many Australian supplies use chloramine, a conditioner is the safer choice, and it works straight away.
Is bottled water good for fish?
Not usually. Spring water is safe but varies in minerals, and mineral or sparkling water can harm fish. Treated tap water is cheaper to keep stable.
What water to use for fish tank set-up on day one?
Treated tap water, the same as for water changes. Fill the tank, add conditioner for the full volume and start cycling before any fish go in.
