Australia’s drinking water guidelines are built on the assumption that you drink two litres a day. That number sits inside the formula behind every chemical limit in the guidelines. If you train hard, work outside, or drink more on purpose, you are not the person those limits were calculated for. You are running more water through your body than the maths allows for.
Quick answer: Yes. The Australian Drinking Water Guidelines assume an adult drinks two litres a day and weighs 70 kilograms. Every chemical limit is worked back from those two numbers. NHMRC’s own nutrition advice tells adults to drink more than that. Anyone on four or five litres a day is going through the assumed volume twice over.
Key takeaways
- Every chemical limit in the Australian Drinking Water Guidelines is calculated assuming you drink two litres a day and weigh 70 kilograms.
- NHMRC’s own Nutrient Reference Values put adequate fluid intake at 2.6 litres a day for men and 2.1 litres for women. Active people in hot climates need more again.
- Ninety minutes of training can add 600 to 1,200 millilitres on top of that, before heat gets counted.
- The guidelines admit you also take chemicals in through your skin in the bath and the shower, then leave that out of the calculation on purpose.
- The average Australian adult drinks about 1.1 litres of plain water a day. The assumption sits above most people and well below anyone optimising.
- The safety factors are still in there. Drinking more thins your margin, it does not push you across a line into harm.
A guideline value is a concentration limit that is calculated rather than measured. Someone takes a dose that caused no effect in testing. They divide it by a large safety factor. Then they work out what strength in water would deliver that dose over a lifetime. To do that last step you have to decide how much water the average person drinks. In Australia, that decision was two litres.
The guidelines were not written for someone drinking four litres a day
The limits assume a fixed daily volume, so your actual exposure scales with what you actually drink. Two people on the same mains supply, in the same street, can be taking in very different amounts of the same compound. The water is identical. The dose is not.
Take trihalomethanes (THMs), the by-products that form when chlorine meets organic matter in the mains. The Australian limit is 0.25 mg per litre. At the assumed two litres a day, that limit works out to a daily budget of 0.5 mg.
Now put a real number against it. Water Corporation’s published data has West Yokine averaging 0.139 mg per litre. At two litres a day you are taking in 0.278 mg, comfortably inside the budget. At four litres you are at 0.556 mg, which is past it. Same tap, same water, different person.
Not every compound behaves that way, and it is worth being straight about that. Free chlorine has an Australian limit of 5 mg per litre. That is a concentration ceiling, not a daily total, so it does not shift depending on how much you drink. I have tested more than 100 Perth homes on a Spin Touch photometer. Free chlorine at the tap runs 0.7 to 1.2 mg per litre, well under that ceiling regardless of volume. The margin is thin on by-products and wide on chlorine itself.
Where the two litre number actually comes from
It comes from the formula used to set the limits, and NHMRC publishes it openly. The
Australian Drinking Water Guidelines state it plainly: “The amount of water consumed by an adult each day is assumed to be 2 L.”
The same section sets the average Australian adult at 70 kilograms and applies safety factors that commonly run from 100 to 1000. It also says something most people never read. Varying those assumptions “could raise or lower the resultant value by a factor of 10 or more”. Every limit therefore carries what NHMRC itself calls a degree of fuzziness.
That is not a criticism of the guidelines. It is how risk-based limits get built anywhere in the world, and the WHO uses the same two litre figure. The point is narrower. A limit is a statement about a concentration paired with an assumed volume. Change the volume and you have changed the statement.
NHMRC’s own advice is to drink more than two litres
The same body that sets the two litre assumption publishes nutrition advice telling you to drink more. NHMRC’s
Nutrient Reference Values put adequate fluid intake for adult men at 2.6 litres a day, about ten cups. For adult women it is 2.1 litres, about eight cups.
Those figures cover all fluids, so tea, coffee and milk count towards them. If you drink mostly plain water, you are pulling close to the whole amount out of your tap.
The same document adds a line worth sitting with. Adults living or working in extremely hot climates may need more than those amounts to stay hydrated, especially if they are very active. That describes a lot of Australia for a lot of the year.
What Australians actually drink, and why the average is not you
Most Australians drink less than the guideline assumes. That is exactly why the assumption survives without argument. The
Australian Bureau of Statistics put average plain water consumption, tap and bottled together, at 1,064 millilitres a day in its national nutrition survey. For adults aged 19 to 50 it peaked at 1,264 millilitres.
So the typical adult is drinking a bit over half what the guidelines assume. For that person the built-in margin is bigger than it looks on paper.
Averages hide the ends, though. The same survey found the top ten per cent getting through at least 1,917 millilitres of plain water. That is before anyone trains. If you are reading an article about water quality, you are almost certainly in that top group rather than near the middle. The guideline’s assumption was never aimed at you.
Training adds a litre before you have thought about it
Exercise is where the numbers move fastest. Victoria’s
Better Health Channel puts 400 to 800 millilitres an hour of exercise as a suitable starting point. Adjust it for climate, sweat rate and tolerance.
Run that through a normal week. A ninety minute session at the middle of that range is another 900 millilitres. Add it to the 2.6 litre baseline for men and you are at 3.5 litres on a training day. Push into a Perth summer, or a job on a roof, and it climbs again.
Plenty of people in the health and performance world target a gallon a day, which is 3.8 litres. Do that and you are drinking almost double the volume every Australian limit was calculated against.
| Who |
Daily water |
Against the 2 litre assumption |
| The guideline’s assumed adult |
2.0 L |
The baseline everything is worked back from |
| Average Australian adult, plain water (ABS) |
1.1 L |
About half |
| NHMRC adequate intake, women |
2.1 L of fluids |
Roughly the same |
| NHMRC adequate intake, men |
2.6 L of fluids |
About 1.3 times |
| Top ten per cent of drinkers (ABS) |
1.9 L plain water and up |
Approaching it on water alone |
| Baseline plus a 90 minute session |
3.5 L |
About 1.75 times |
| Common one gallon target |
3.8 L |
Nearly double |
The assumption nobody mentions is your shower
There is a second assumption in the same formula, and it matters more than the first. The guidelines only count what you drink.
NHMRC is open about this. The same section says exposure is mostly through drinking the water. Then it adds that you also take some in through your skin in the bath, and breathe some of it in the shower. It then explains the decision. The lower figure is used anyway “because it provides a higher margin of safety”.
That wording does two things at once. It confirms the shower is a real exposure route. It also confirms the limit is a drinking-water number by design. The rest is handled by the safety factor rather than counted.
That is a reasonable way to write a national standard. It is a poor way to think about your own house. You do not just drink your water. You stand in it hot, with the door shut, most days of your life. We have worked through what that means in full in a
dedicated article on whole house filtration.
What this means for the water coming into your house
If your exposure scales with volume, the fix is to lower the concentration at the point everything is fed from. That is what ZERO filtration is built to do. It goes in where the mains enters the property. Every tap and every shower in the house then runs filtered water, not just one outlet in the kitchen.
ZERO filtration reduces free chlorine, THMs, haloacetic acids (HAAs), VOCs, pesticides, taste and odour, and offers general reduction of heavy metals. Those are the compounds most affected by how much you drink. Chlorine and its by-products are also the ones you meet in the shower.
Capacity is what makes that hold up over time. Carbon is a bucket, and buckets fill. ZERO carries up to 18 kilograms of combination media. A standard 10 inch whole-house cartridge holds about one kilogram. That is far more bucket to fill before performance drifts. It backwashes itself every week and holds that schedule through a power cut. That keeps the bed clean, instead of letting water carve an easy path through the middle.
It is WaterMark Certified WM-032536 against AS 3497 and installs like a hot water unit. Media service life runs for years between replacement. If you are the person drinking four litres a day, this is the input you have never audited. You can see
the full specification for the ZERO Filter, or read how
filter capacity runs out if you want the mechanism behind that bucket.
Where this argument stops
This is not a reason to drink less water. Dehydration of as little as two per cent of body weight already impairs how you perform. NHMRC sets no upper limit on water intake at all. Drink what you need.
A few honest constraints on the argument itself:
- The safety factors are still doing their job. Doubling your intake thins the margin between you and the no-effect dose. It does not put you past it.
- Australian mains water generally sits well under the limits rather than at them. Most people have headroom on top of the safety factor.
- The margin is not uniform. It is tight on by-products in some suburbs and very wide on free chlorine everywhere.
- ZERO needs a plumber and a place at the main. That is the cost of treating every outlet instead of one.
- The media is a consumable. It does a real job for years, then it gets recharged.
If your interest is hardness and scale rather than what you are drinking, that is a different question with a different answer. Start with
the difference between filtration and softening instead.
Frequently asked questions
Are the Australian drinking water guidelines safe if I drink more than two litres a day?
They are still protective, but your margin is smaller than it was designed to be. The limits are calculated at two litres a day for a 70 kilogram adult, with safety factors commonly between 100 and 1000 on top. Drinking four litres does not push you past a harm threshold. It halves the headroom the calculation gave you.
How much water should an Australian adult drink a day?
NHMRC’s Nutrient Reference Values put adequate fluid intake at 2.6 litres a day for men and 2.1 litres for women. That counts all fluids, including tea, coffee and milk. Very active people need more than that, as does anyone living or working in extremely hot conditions. There is no upper limit set for water intake.
Does drinking more water mean I take in more chlorine and by-products?
Yes, in direct proportion. Strength multiplied by volume gives you the dose, so doubling the volume doubles the dose from the same tap. That is why the two litre assumption matters to high-volume drinkers and barely matters to anyone drinking a litre a day.
Do the guidelines account for the water I absorb in the shower?
No, not directly. NHMRC acknowledges that you take some in through your skin in the bath and breathe some of it in the shower. It then uses the lower drinking-only figure on purpose, because that leaves a bigger safety margin. The exposure is real and it is covered by the safety factor rather than counted in the calculation.
Should I drink less water to reduce my exposure?
No. The health cost of under-drinking is immediate and well established, and the guidelines are conservative by design. Keep drinking what your body needs and lower what is in the water instead. Speak to your GP about your own fluid intake if you have a medical condition that affects it.
Why does the guideline assume 70 kilograms?
It is the figure NHMRC uses for an average Australian adult. Canada and other developed countries use the same one. The WHO uses 60 kilograms, which reflects lower adult weights in developing countries. A heavier assumed weight slightly raises the resulting limit. The Australian numbers are therefore marginally less strict than the WHO equivalents.
About the author
Sam Licastro comes from a plumbing trade background and previously managed at an ASX listed plumbing supplier. He tests water in Perth homes and built BASELINE Water around what those results kept showing. BASELINE ZERO is WaterMark Certified WM-032536 against AS 3497. You can read more
about the people behind BASELINE.
If you want to know what your own water is carrying, that starts with a reading, not a guess.
Get in touch and we will work through it, or see what
chlorine turns into on the way to your tap first.
