If all you want is better tasting water at the kitchen sink, you do not need a whole house filter. If you want the water treated before it reaches anything in your home, you do. The useful way to decide is not to compare products. It is to work out where you actually meet your water, because you meet a lot more of it than you drink.
Quick answer: It comes down to exposure, not taste. Australia’s chemical limits for drinking water are calculated on what you swallow and nothing else. NHMRC says openly that you also take some in through your skin, and breathe some in the shower. Then it leaves both out of the sums on purpose. Treating the water where it enters the property is the only way to cover all three.
Key takeaways
- Every chemical limit in the Australian Drinking Water Guidelines is worked out on 2 litres a day swallowed, and nothing else.
- NHMRC states that skin absorption in the bath and inhalation in the shower both happen. It then uses the drinking-only figure anyway, because that leaves a bigger safety margin.
- In a shower, 56 per cent of the chloroform in the water leaves the water and goes into the air you are breathing.
- Peer reviewed research found that inhalation during a normal 10 to 15 minute shower contributes significantly to your total chloroform dose.
- The same researchers noted that standard water risk assessments count swallowing only. Showering raises how much ends up in your body by two further routes.
- A filter at one outlet treats the water at that outlet. Only treating water at the main covers every tap and the shower.
A whole house filter, also called a point of entry system, is plumbed in where the mains supply enters your property. Every outlet in the house then runs treated water. That is the whole difference. Not what it catches, but how much of your water it gets to see.
You meet your water in three places, not one
Ask most people how much tap water they use and they think about drinking. That is the smallest part of it.
You swallow it. You stand in it, hot, with your pores open and most of your skin exposed. And you breathe the air in a small closed room while it is being sprayed through the air at high pressure. Three routes, every day, from the same pipe.
The reason this matters commercially is simple. Where you treat the water decides which of those three you have covered.
The guidelines only count what you swallow
This is the part that surprises people, and it comes from the regulator rather than from us. The
Australian Drinking Water Guidelines set out exactly how every chemical limit is calculated, and the calculation is built on drinking.
NHMRC then addresses the other routes directly. It states that exposure is mostly through drinking the water. Then it adds that skin absorption during bathing, and inhalation in a shower, can also occur. Then it explains what it does about that. The lower drinking-only proportion is used anyway, in its words, “because it provides a higher margin of safety”.
That wording does two separate things. It confirms the shower is a real exposure route. It also confirms the number in the guidelines was never meant to describe it. The rest is covered by the safety factor instead of being counted.
That is a defensible way to write a national standard. It is a poor way to decide what to do in your own house.
What is actually happening in a ten minute shower
Independent researchers have measured this, and the numbers are not small.
Work published in the
Journal of Exposure Science and Environmental Epidemiology measured what a shower does. It found 56 per cent of the chloroform in the water leaves the water and enters the air. Chloroform is a trihalomethane, or THM, one of the by-products that forms when chlorine meets organic matter in the mains. The same study concluded that a typical 10 to 15 minute shower contributes significantly to your total chloroform dose.
Skin is the other route. A companion study on
dermal uptake during bathing opens by calling skin contact with THMs an established exposure route. Not a theory. Established.
Putting the routes side by side,
earlier work in Environmental Health Perspectives is blunt about the gap. Traditional risk assessments consider swallowing only, it says. Showering has been shown to increase the amount of certain chemicals in the body, through both breathing and skin. Every one of the three routes contributed to total exposure.
Hot water makes it worse, not better. Heat drives more of it out of the water and into the air, and warm skin takes up more than cool skin. A long hot shower in a closed bathroom is close to the worst case, and it is also what most people do every day.
| How you meet your water |
Counted in the guideline calculation? |
| Drinking and cooking |
Yes, at 2 litres a day |
| Skin contact in the shower or bath |
No, acknowledged then excluded |
| Breathing it in during a shower |
No, acknowledged then excluded |
There is a second assumption worth knowing about
The guideline also assumes you drink 2 litres a day. That is less than NHMRC’s own nutrition advice tells adults to drink. If you train, work outside, or just drink more on purpose, the sums were not written for you. That is a whole argument in itself and we have
worked through it separately.
Worth knowing, but it is not the point here. Even if you drink exactly the 2 litres the guideline assumes, you are still meeting your water twice more every day in the bathroom.
What treating the water at the main actually changes
A filter treats what passes through it. Put it under one sink and it treats that sink. Put it where the mains enters the property and every outlet in the house is downstream of it, including the shower.
That is how
ZERO filtration is set up. It installs at the water main. The water reaching your kitchen tap, your bathroom basin and your showerhead has all been through the same media bed. ZERO filtration reduces free chlorine, THMs, haloacetic acids (HAAs), VOCs, pesticides, taste and odour, and offers general reduction of heavy metals. Chlorine and its by-products are exactly the compounds the shower research is concerned with.
Capacity is what keeps that true beyond the first year. Carbon is a bucket, and buckets fill. ZERO carries up to 18kg of premium carbon and KDF 55. A standard 10 inch whole house cartridge holds about 1kg, and stacking three of those small cartridges together does not fix that, which is the trap in
triple filter systems. Eighteen times the media means eighteen times the bucket, which is what lets it run for years between replacement rather than months. When a bucket does fill, nothing announces it, which is
what a spent filter quietly does to your water.
Volume is only half of it. Media that never moves packs down. Water then carves an easy path straight through the middle, while the rest of the bed does nothing. ZERO backwashes itself every week and holds that schedule through a power cut, so the bed stays open and performance stays more consistent. It is WaterMark Certified WM-032536 against AS 3497 and installs like a hot water unit.
Running a café, salon or restaurant? The same setup at the main covers your basins, coffee machine and kitchen taps. See
BASELINE ZERO for business.
When you do not need one
There are houses where this genuinely is not the issue, and it is worth saying so plainly.
If you are on rainwater tanks and nobody is chlorinating them, there is no chlorine, so there is nothing here to form by-products. This argument does not apply to you. Whether you want filtration for other reasons is a separate conversation.
If it is scale, chalky kettles and spotted glassware bothering you, that is hardness, which is
a different problem with a different fix.
And if you are on mains water, here is what doing this properly actually costs:
- ZERO goes in at the water main, so it needs a licensed plumber and a spot outside about the size of a hot water unit. That is the price of treating every outlet instead of one.
- The media is a consumable. It works for years and then it gets recharged, because catching things is what fills it up.
- It reduces what is in the water, it does not sterilise it. Your supply is already disinfected and should stay that way.
Frequently asked questions
Do I need a whole house water filter if I already filter my drinking water?
It depends whether drinking is the only exposure you care about. A filter at one tap treats the water at that tap, which covers what you swallow. It does not change the water in your shower. Research has established both skin absorption and inhalation as real routes for chlorine by-products. To cover those, the filter has to sit upstream of the whole house.
Do the Australian drinking water guidelines account for shower exposure?
No, and NHMRC does not hide it. The guidelines state that skin absorption during bathing and inhalation in a shower can occur. They then use the lower drinking-only proportion, because it provides a higher margin of safety. The exposure is treated as real but is handled by the safety factor rather than counted in the calculation.
Is chlorine actually absorbed through your skin in the shower?
The research says the by-products are. A study on dermal uptake during bathing states that skin contact with THMs in chlorinated drinking water is an established exposure route. Hot water increases it, because heat raises how much comes out of the water and warm skin takes up more than cool skin.
Does a whole house water filter reduce chlorine in the shower?
That is the main thing it does that a filter at one tap cannot. ZERO filtration sits at the water main, so the shower is downstream of it like every other outlet. The water arriving at the showerhead has already been through the media. ZERO filtration reduces free chlorine, THMs and HAAs among others.
Is a whole house water filter worth it on Australian mains water?
Australian mains water is regulated, disinfected and safe to drink, and chlorination is the reason waterborne disease is effectively gone here. None of that is in question. What a whole house filter changes is how much chlorine and how many by-products you meet across a whole day. Every tap and the shower, rather than the glass alone.
How long does the media in a whole house filter last?
It depends entirely on how much media there is and how hard the water works it. A standard 10 inch whole house cartridge holds about 1kg, which buys you months. ZERO holds up to 18kg and runs for years between replacement. Capacity is what turns an unknown into a service interval you can plan around.
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.
This article is general information, not medical advice. If you have a specific health concern about your water, speak to your GP or your state Department of Health.
If you want to know what your own water is carrying, that starts with a reading rather than a guess.
Tell us your suburb and we will look it up, or start with what
chlorine turns into on the way to your tap.
