Is the chlorine in Australian tap water safe?

Yes. The chlorine in Australian tap water sits well under the level anyone considers a health risk, and it is the reason nobody in this country worries about getting sick from the tap. What almost nobody explains is what happens after that. Chlorine does not just sit in the pipe waiting for you. It reacts, and what it turns into on the way to your house is a different question altogether. Quick answer: The safe limit for chlorine in Australian tap water is 5 mg/L. We have tested more than 100 Perth homes and free chlorine comes in at 0.7 to 1.2 mg/L, so you are nowhere near it. The chlorine itself is not the problem. The problem is what chlorine turns into on the way to your house. A disinfection by-product is a chemical that forms when a disinfectant reacts with something already in the water. Nobody puts them there. They get made in the pipe, after treatment, out of two things every chlorinated supply already has in it.

What chlorine turns into once it is in the mains

Chlorine does not stay chlorine. It is there to kill things, so it is reactive by design, and it does not stop being reactive once the bugs are dead. Your water carries organic matter. Not sewage, just the natural stuff that washes off soil and leaves into a catchment. Treatment takes most of it out. It never takes all of it out. Chlorine finds what is left and reacts with it. That reaction makes brand new chemicals that were not in the water and were never added to it. The two families worth knowing are THMs and haloacetic acids (HAAs). Chloroform is the one you have heard of. They get called disinfection by-products, because that is what they are, the by-product of making water safe. Here is the part that matters. The reaction does not finish at the treatment plant. Chlorine and organic matter stay in the same pipe together for hours or days, so the reaction keeps going the whole way to your house. Your water is still changing while it travels.

How much is actually in Australian tap water?

More than most people would guess. According to the NHMRC’s fact sheet on THMs, THM levels in major Australian mains supplies run up to 0.6 mg/L. The safe limit is 0.25 mg/L. Read the rest of the guideline before you react to that. The ADWG also says levels that spike for a day or two a year, as high as 1 mg/L, are unlikely to pose a significant health risk. A water utility sitting at the top of the range in a bad week is not doing anything wrong. HAAs get discussed far less. The ADWG tracks three of them, with limits of 0.1 to 0.15 mg/L, and Australian water generally comes in under those. One more line from the ADWG is worth repeating. A high THM reading can be a sign that other by-products are in there too, ones nobody routinely tests for or reports.

Are THMs and HAAs dangerous?

The honest answer is that the evidence is mixed, and the regulators say so plainly. The International Agency for Research on Cancer calls chloroform possibly carcinogenic to humans. That sounds worse than it is. It means the animal evidence is there but the human evidence is not, and IARC says so directly. Chlorinated drinking water as a whole it will not classify at all, because the human data is not good enough either way. The animal tumours behind that rating turned up at doses nowhere near what comes out of a tap. The ADWG took the highest dose that caused no effect at all in testing, then divided it by 100 to set the limit. That is the margin you are working with. So this is not a reason to be frightened of your tap. It is a reason to understand what the guideline actually is. It is a risk-management number with a deliberate margin built into it, not a line where water flips from harmless to harmful. The ADWG is direct about where the balance sits. Action to reduce THMs is encouraged, but it must never compromise disinfection, because undisinfected water is a far greater risk.

Why your suburb matters more than your city

Compliance is reported across a network. Your tap is not the network. Water Corporation publishes its drinking water quality results locality by locality, which makes Perth one of the few Australian cities where you can see this properly rather than guess at it. The 2024-25 health-related data for the Perth region shows THM levels varying by more than twenty-five times across the same metropolitan supply.

Perth locality	Mean THMs (mg/L)	Highest single reading (mg/L)	ADWG guideline (mg/L)
West Yokine	0.139	0.180	0.25
Mirrabooka	0.125	0.150	0.25
South Perth and Kewdale	0.118	0.160	0.25
Melville	0.061	0.088	0.25
Mundaring	0.021	0.028	0.25
Two Rocks	0.005	0.009	0.25

Every one of those suburbs passed. That is the point, not a get-out. Two houses can both be on water that passed every test, and one of them is getting twenty-five times what the other is. Two things drive it. How far your water has travelled, because the reaction keeps going the whole way and longer trips mean more time to react. And where your water came from, because a bore carrying almost no organic matter gives chlorine almost nothing to work with. That is why Two Rocks reads so low. This applies everywhere, the numbers just change. If your water supplier publishes results suburb by suburb, go and find yours instead of taking the citywide average.

The guideline assumes you drink two litres a day

Every limit in the ADWG is a number per litre. To get there, somebody had to decide how many litres you drink. They picked 2 a day. That figure sits underneath the THM limit and the chlorine limit both. Now look at what the same organisation says about drinking water. NHMRC’s Nutrient Reference Values put adequate fluid intake at 2.6 litres a day for men and 2.1 for women, and add that if you are very active or working in real heat you need more than that. So the mob who write the water limits also tell you to drink more water than those limits assume. There is a fuller breakdown of how that two litre assumption is calculated, and what it means if you drink four, in its own article. Do the sums. Two litres of water sitting right on the 0.25 mg/L limit gives you 0.5 mg of THMs a day, and 0.5 mg is the number the whole thing was built around. Drink 4 litres, which is nothing unusual if you train through a Perth summer, and West Yokine’s average of 0.139 mg/L puts you at 0.556 mg. You are past what they planned for, on water that passed every test. Be clear on what that is and is not. You have not crossed a line where harm starts. That safety factor of 100 is still sitting under you and it is deliberately generous. What has changed is your margin. It is thinner than the number on the page looks, and it gets thinner every extra litre you drink. None of that is an argument for drinking less water. It is an argument for caring what is in the water you drink a lot of.

Is the chlorine itself safe to drink?

Yes, at Australian supply levels. The ADWG health guideline for total chlorine is 5 mg/L. Across the country the ADWG says free chlorine in the mains runs anywhere from 0.1 to 4 mg/L, and calls 0.2 to 0.5 typical. That typical figure does not describe Perth. We have tested free chlorine at the tap in more than 100 Perth homes on a Spin Touch photometer. It reads 0.7 to 1.2 mg/L, over and over. Still a fraction of the 5 mg/L limit. Two to three times what the guideline calls normal. The ADWG tells you why, if you read far enough. Most people start smelling chlorine at about 0.6 mg/L, and some pick it up at 0.2. The ADWG then says plainly that water authorities may have to go over that smell threshold to keep enough chlorine in the pipe to do its job. Perth pushes water a long way through a hot climate, so it gets dosed harder, so you smell it. That is not a stuff-up. That is the system working, and it is why your water tastes the way it does. Chlorine on its own has a good safety record. The ADWG records 150 people drinking water at 50 mg/L while a main was being disinfected, with no ill effects. Soldiers have drunk water at 32 mg/L for months, also with no ill effects. Those are dozens of times the level you would ever see at home, and nothing happened. So the chlorine is not the problem. What it leaves behind is the more interesting question.

What you can actually do about it

The ADWG names the fix itself. Carbon. It catches THMs after they have formed, and it catches the organic matter that makes them in the first place. The thing to understand about carbon is that it does not destroy anything. It grabs and holds. So it is a bucket, and buckets fill. Once the carbon is full it quietly stops catching, and everything it used to catch goes straight past into the house. That is what a spent filter actually does to your water. Nothing looks different. Nothing beeps. This is where ZERO filtration is built differently. ZERO carries up to 18kg of combination media filtration. A standard 10 inch whole-house cartridge holds about 1kg. Eighteen times the media means eighteen times the bucket, which is why ZERO runs for years between replacement instead of months. ZERO filtration reduces free chlorine, THMs, HAAs, VOCs, pesticides, taste and odour, and heavy metals. Size is only half of it. Media that never moves packs down, and water carves itself an easy path straight through the middle while the rest of the media sits there doing nothing. ZERO backwashes itself every week, lifting the media and letting it settle again so all of it stays working and performance stays more consistent. It remembers its schedule for seven days, so a power cut does not throw it out. It is a point of entry system. It goes in at the water main, so every outlet in the house is treated, not just the one with a jug sitting next to it, including the shower, which the drinking water guidelines do not count. If you are getting through 3 or 4 litres a day, every one of those litres has already been through it. It installs like a hot water unit, it is WaterMark Certified WM-032536 against AS 3497, and it ships Australia-wide, same day across Perth metro on orders before 10am. For some businesses chlorine is a daily cost, not just a taste. At the salon basin it can leave blonde colours looking dull or green, and in a café it carries through into the coffee. Here’s how BASELINE ZERO works for cafés, salons and restaurants.

When chlorine by-products are not your problem

There are households where this genuinely is not the issue. If you are on rainwater tanks and nobody is chlorinating them, there is no chlorine, so there is nothing here for it to turn into. This one does not apply to you. Whether you want filtration for other reasons is a separate conversation, and scale and hard water in particular are a different problem with a different fix. If you are on mains water, here is what it honestly costs to do this properly:

• ZERO goes in at the water main, so you need a licensed plumber. It is not something you screw on yourself on a Saturday. That is the price of treating every tap in the house instead of one.
• The media is a consumable. It fills up eventually, because that is how catching things works. ZERO runs for years between replacement, which is what carrying 18kg instead of 1kg buys you.
• It takes up space outside, about the same as a hot water unit. Anything holding that much media has to go somewhere.

Frequently asked questions

Do THMs in tap water cause cancer?

Nobody has shown that they do in humans. The International Agency for Research on Cancer calls chloroform possibly carcinogenic, based on animal tests at doses far higher than anything in tap water, and it will not classify chlorinated drinking water as a whole because the human evidence is not there. The safe limit of 0.25 mg/L was then set 100 times lower again for safety. If you have a specific health concern, speak to your GP.

Do the drinking water guidelines account for people who drink a lot of water?

Only by assuming everyone drinks the same amount. Every limit in the Australian Drinking Water Guidelines is worked out on 2 litres a day for a 70 kg adult. NHMRC’s own nutrition advice says men should get 2.6 litres of fluid a day and women 2.1, and that very active people in the heat need more again. Drink well over 2 litres and you take in proportionally more of whatever is in your water, so your safety margin is thinner than the printed number suggests.

Is it safe to drink chlorinated Australian tap water every day?

Yes. Australian mains water is regulated against the Australian Drinking Water Guidelines, and the chlorine in it sits well under the 5 mg/L safe limit. Chlorination is also the reason waterborne disease is effectively gone from Australian supplies. The ADWG is blunt about it: cutting by-products must never come at the cost of disinfection. The same guidelines cover dozens of other compounds too, including what the testing for PFAS actually looks like.

Do THM levels change through the year?

They are not a fixed number. THMs keep forming for as long as chlorine and organic matter sit in the same pipe, so the level at your tap moves around. Water Corporation’s Perth results show a range at almost every suburb rather than one figure. West Yokine ran from 0.088 to 0.180 mg/L across 2024-25.

Does boiling tap water reduce chlorine and THMs?

Partly, and not evenly. Chlorine and some THMs will come off with the heat, which is why the ADWG lists blowing air through water as one way of dealing with them. HAAs do not evaporate, so boiling does nothing for those. And boiling only ever fixes what is in the kettle, not the water at every other tap in the house.

Why does my tap water smell like a swimming pool?

Because your nose picks up chlorine long before it gets anywhere near unsafe. Most people smell it at about 0.6 mg/L and some at 0.2, against a safe limit of 5 mg/L. The ADWG says water authorities sometimes have to push past that smell threshold to keep enough chlorine in long mains, which is why the smell changes from suburb to suburb and season to season.

About the author

Sam Licastro is the founder of BASELINE Water, who comes from a plumbing trade background and previously managed at an ASX listed plumbing supplier. BASELINE ZERO is WaterMark Certified WM-032536 against AS 3497. This article is general information, not medical advice. If you have a specific health concern about your drinking water, speak to your GP or your state Department of Health. If you want to know what your own water is running at, tell us your suburb and we will look it up for you. If you already know you want it handled, see how ZERO works.