Do I Need a Water Filter or a Water Softener?

If you supplement magnesium, track your electrolytes and read the label on everything else you put in your body, it is worth knowing what your water treatment is doing to your water. Filtration and softening solve different problems. Filtration works on dissolved chemistry, and what it reduces depends entirely on the media inside it. Softening works on calcium and magnesium. Confuse the two and you can end up paying to strip minerals out of water that barely had any to begin with. Quick answer: Test your water first, it costs nothing. Under roughly 120 mg/L, softening is not your problem, minerals are worth keeping, not stripping out by default. If your number comes back high, the real risks are scale, appliance wear and shortened equipment life, not the minerals themselves. Hardness is the concentration of dissolved calcium and magnesium salts in water, measured in milligrams per litre as calcium carbonate. That one number decides most of this question, and almost nobody knows theirs before they buy.

Why stripping minerals from soft water is the wrong move

Calcium and magnesium are not contaminants. They are dietary minerals dissolved in your water, and taking them out of water that has very little to start with is the one genuinely counterproductive thing available here. Food supplies most of your intake. The World Health Organization puts the typical dietary contribution at over 80 percent of the daily total, with drinking water contributing 5 to 20 percent for both minerals. That share moves with volume, and most people drink more than the guidelines assume. Not the main source, but not a rounding error either, and WHO notes that because of dietary habits many people already fail to reach recommended intakes of one or both. Be careful with the health claims made in this space, including by people selling water treatment. WHO’s actual conclusion is measured: although there is some evidence from epidemiological studies for a protective effect of magnesium or hardness on cardiovascular mortality, the evidence is debated and does not prove causality, and WHO proposes no minimum or maximum guideline values for minerals. The Australian Guidelines are similarly careful, noting the data are inadequate to conclude the association is causal. Anyone telling you hard water prevents heart disease is going further than the evidence does. What the evidence does support is more practical. WHO is explicit about what softening does to the water you drink: consumption of calcium and magnesium will be lower unless the water consumed is not softened or is remineralised. It follows that up with a recommendation that ought to be standard practice and is not, which is that users of these devices should be made aware of the changes in mineral composition that arise and the possible consequences for total nutrient intake. There is a second reason not to over-soften. Both WHO and the Australian Guidelines note that soft water which has not been stabilised is more aggressive toward pipework, and corrosion is how metals such as copper and lead end up in water that left the treatment plant without them. Driving hardness to zero across a whole house is not a neutral act.

What WHO actually recommends doing about it

This is the part worth knowing before you buy anything, because it describes a capability rather than a product. WHO’s suggested remedies for households that soften are, in its own words, to soften only the hot water line at the entry to the water heater, or for manufacturers to provide a suitable bypass of a portion of this water to maintain some level of these minerals in the water actually consumed, for example at a kitchen tap. The international health authority’s answer to the mineral problem is not to stop softening. It is to keep some minerals in the water, deliberately, by blending. That requires a system with a control that can be set. Which is the whole argument in one line: hardness is a level to be set, not a contaminant to be driven to zero.

Why you should know your number before you install anything

Water treatment is a modification to your household inputs, and it deserves the same discipline you would apply to anything else you are optimising. You would not change a supplement protocol without knowing your baseline. Water is no different. The failure mode is quiet. Someone health conscious decides to sort out their water, buys a system on the assumption that treated is better than untreated, and ends up with softened water in a suburb that was already soft. Nothing dramatic happens. They simply paid to take out minerals that were doing no harm, while supplementing one of them separately. The fix is not to avoid treatment. It is to establish your hardness figure first, because it tells you which of the two problems you actually have, or whether you have either.

What counts as hard water in Australia?

There is an official answer, and it is more useful than the marketing version. The Australian Drinking Water Guidelines set the threshold at 200 mg/L: total hardness as calcium carbonate should not exceed 200 mg/L to minimise undesirable build-up of scale in hot water systems. Note what that number is actually derived from: difficulty getting a lather with soap, and scale building up in hot water pipes and fittings. It is a scale and nuisance threshold, not a health limit. The Guidelines band hardness into four ranges.

Hardness	ADWG description	What it means at home
Under 60 mg/L	Soft, but possibly corrosive	No scale. Low mineral content, and unstabilised soft water is more aggressive toward pipework
60 to 200 mg/L	Good quality	The target range. Scale becomes noticeable toward the upper end
200 to 500 mg/L	Increasing scaling problems	Visible scale, shortened appliance life, more soap and detergent
Over 500 mg/L	Severe scaling	Rare on Australian mains supplies

Two things there are worth pausing on. The first is that under 60 mg/L is not described as ideal. It is described as soft but possibly corrosive, and the Guidelines note separately that soft water below about 75 mg/L may adversely affect mineral balance. European standards go further and treat a minimum of 60 mg/L as desirable. Low hardness is a condition with its own tradeoffs, not the finish line. The second is the spread. Total hardness in major Australian reticulated supplies runs from about 5 mg/L to about 380 mg/L. There is no meaningful national figure, and no advice pitched at “Australian water” survives that range.

A worked example: how much hardness varies inside one city

Perth is a useful case study because Water Corporation publishes hardness at locality level, which not every utility does. The pattern it shows is why averages are worthless. These are the mean figures from the Drinking Water Quality Annual Report for 2024 to 2025, banded against the ADWG ranges above.

Supply locality	Mean hardness	ADWG band
Two Rocks	228 mg/L	Increasing scaling problems
Yanchep	198 mg/L	Good quality, top of the band
Neerabup	190 mg/L	Good quality, top of the band
Wanneroo	125 mg/L	Good quality
Mirrabooka	124 mg/L	Good quality
West Yokine	123 mg/L	Good quality
Whitfords	113 mg/L	Good quality
Mt Yokine	108 mg/L	Good quality
Mt Hawthorn	106 mg/L	Good quality
South Perth and Kewdale	94 mg/L	Good quality
Mt Eliza	57 mg/L	Soft, possibly corrosive
Hamilton Hill	56 mg/L	Soft, possibly corrosive
Melville	54 mg/L	Soft, possibly corrosive
Mandurah	50 mg/L	Soft, possibly corrosive
Dwellingup	29 mg/L	Soft, possibly corrosive

Nearly eight times the hardness at one end of a single metropolitan area compared with the other, with localities falling into three different ADWG bands. A household at Two Rocks and a household at Mandurah are not having the same experience. The pattern is geographic and it generalises. The Guidelines note that high total hardness may be a problem for supplies reliant on groundwater, while surface waters can generally be expected to have acceptable values. Zones drawing on groundwater sit at the top, because water moving through limestone and soil picks up calcium and magnesium. Zones carrying more desalinated or surface water sit at the bottom. Wherever you are in Australia, your figure is largely a function of which source feeds your suburb. Worth noting for the softer end of the country. Sydney and Melbourne supplies are widely reported as soft, and much of that water sits below the 75 mg/L point where the Guidelines flag possible effects on mineral balance. The argument for not stripping minerals further is strongest exactly where people assume they have nothing to think about.

How to find your own figure

Your water utility is the source, though how easily you can find it varies. Most large Australian utilities publish water quality data, often as an annual drinking water quality report with tables by supply zone or locality. Water Corporation in WA publishes locality level hardness. Others report by supply zone, some publish summaries rather than full tables, and Melbourne is served by several retailers rather than one, so which report applies depends on your address. Search your utility’s name with “water quality” and look for hardness, reported as milligrams per litre of calcium carbonate. Parts per million is the same number. If your area is not broken out separately, or you cannot tell which supply zone you are in, ring them. They hold the figure whether or not it is easy to find on the website.

What is the difference between filtration and softening?

Filtration works on dissolved chemistry, and this is where the word “filter” does a lot of hiding. It describes a category, not a capability. What a given system actually reduces is determined by the media inside it and how much of it there is, and the range across products is enormous. Some address little beyond sediment and the chlorine you can taste. ZERO filtration is built around a media blend that reaches considerably further into the dissolved chemistry. Taste improving is a consequence rather than the objective, and treating taste as the purpose mistakes a symptom for the job. Softening works on minerals through an entirely different mechanism. Ion exchange resin swaps the calcium and magnesium in your water for sodium, two sodium ions for each divalent mineral ion, so the minerals that form scale are traded for one that does not. A filter will not soften water and a softener will not address the chemistry. Water Corporation puts the first half plainly, noting that calcium and magnesium dissolve into water as it moves through soil and rock and cannot be removed by filtration. Read that as a description of the technology rather than a shortcoming. If your water is not hard, minerals passing through untouched is exactly what you want.

The three things that decide whether a system suits your water

Once you know your number, the specification questions are straightforward. Three are worth asking about anything you are considering.

Factor	Why it matters	What to ask
Media volume	Capacity is a function of how much media sits in the vessel. More media means more water treated before performance falls away, on the same supply	How much media does it hold, and what service life does that give on my hardness and household size?
Regeneration	Media that clears itself on a cycle does not sit loaded between services. Media that only depletes has a shorter working life and a shorter interval	Does it regenerate or backwash on a schedule, and what does that cycle need?
Regulation	Without a control valve there is one fixed outcome for every litre. With one, you set the result rather than accept it	Can I choose how much hardness stays in the water, and what controls that?

Regulation is the one people think about least and should think about most, and it is the one WHO effectively endorses above.

So what do you actually need?

Find your hardness number. Everything else follows from it, and establishing it costs nothing. Under roughly 120 mg/L, softening is not your problem. Your water is inside the band the Guidelines call good quality, and taking minerals out of it moves you toward the range where they flag effects on mineral balance. What remains a live question is the dissolved chemistry, which is a separate matter entirely, and there the answer depends on how far you want that handled. That is what the ZERO Filter is built for. It holds up to 18 kg of premium carbon and KDF 55, around eighteen times the filter material in a standard 10 inch whole house filter, and it backwashes itself weekly so the bed is cleared rather than left loaded. Across the whole house, ZERO filtration reduces free chlorine, THMs, HAAs, volatile organic compounds and pesticides, and reduces heavy metals, with taste and odour improving as a result rather than as the point. What it does not touch is dissolved calcium and magnesium, which in these zones is exactly right. The chemistry goes, the minerals stay. At 150 mg/L and above, you have two problems rather than one. The chemistry is still there, and so is real scale. Filtration handles the first. The second needs ion exchange sized to the load and, more importantly, able to be set. That is what BASELINE ONE is built for. It blends treated water back with untreated, so you set the level that comes out. Calcium and magnesium stay in the water you drink, by design rather than by accident. It regenerates on its own and you top up the salt. One requirement worth knowing in advance: softening resin does not tolerate chlorine well, so dechlorination has to sit ahead of it. The filter is not an optional companion to a softener, it is what protects it. On bore or tank water, none of this applies cleanly. Test before buying anything, because private supplies vary far too much for general advice to be worth much.

What are the tradeoffs?

A tank softener uses salt and water. It regenerates on its own and you top up the salt, and each regeneration sends water to drain. Neither is a dealbreaker, both are real. Softening also raises the sodium and chloride content of the water, because that is the exchange being performed. For most people the amount is minor against dietary intake, but anyone on a medically restricted sodium intake should raise it with their doctor rather than assume. Filtration media is a consumable. It is engineered for years between service rather than months, but it is not permanent. And the honest one about scope: if your water is soft, softening is not your answer. That is a separate question from filtration, which stands on its own reasons. Most of what ZERO filtration reduces cannot be tasted at all, and a whole house system also catches the sediment that turns up after mains work or a burst. Whether that is worth it is a judgement call, but it is not the same judgement as whether you need a softener, and the two get conflated constantly.

Frequently asked questions

Does softening take all the minerals out of my water?

By default it takes out most of the hardness, because ion exchange swaps calcium and magnesium for sodium. The World Health Organization notes that consumption of calcium and magnesium will be lower unless the water consumed is not softened or is remineralised, and suggests either softening only the hot water line or providing a bypass that keeps some minerals in the water actually consumed. A softener with a blend control lets you set the level rather than accept whatever the resin does.

Is it bad to have very soft water?

The Australian Drinking Water Guidelines describe water under 60 mg/L as soft but possibly corrosive, and note that soft water below about 75 mg/L may adversely affect mineral balance. European standards treat a minimum of 60 mg/L as desirable. Unstabilised soft water is also more aggressive toward pipework, which is one route by which metals enter water that left the treatment plant without them.

Do I need a water softener?

Only if your supply zone actually runs hard. The Australian Drinking Water Guidelines treat 200 mg/L as the point of elevated hardness and describe 60 to 200 mg/L as good quality, though scale becomes noticeable toward the upper end of that band. Check your locality’s figure first, because softening water that is already soft achieves nothing useful and moves you toward the range where the Guidelines flag possible effects on mineral balance.

Does a water filter soften water?

No. Filtration works on dissolved chemistry, while hardness is dissolved calcium and magnesium. Water Corporation states that these minerals cannot be removed by filtration. Softening requires ion exchange, which is a separate process. Worth noting that what a filter reduces varies enormously by media: ZERO filtration reduces free chlorine, THMs, HAAs, volatile organic compounds and pesticides, and reduces heavy metals, but that is a function of its media blend rather than something every filter does.

How do I find out how hard my water is?

Your water utility publishes it, usually in an annual drinking water quality report with tables by supply zone or locality. Search your utility’s name with “water quality” and look for hardness, reported as milligrams per litre of calcium carbonate, which is the same as parts per million. If your area is not broken out separately or you cannot tell which supply zone you are in, ring them and ask.

Is Perth water hard or soft?

Both, depending on where you live. Water Corporation’s 2024 to 2025 data shows mean hardness from 29 mg/L at Dwellingup to 228 mg/L at Two Rocks. Northern supply zones drawing on Gnangara groundwater run hard, while southern and coastal zones carrying more desalinated water run soft. There is no single figure for the city, which is why the locality number is the one that matters.

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 concern about mineral intake or a restricted sodium diet, speak to your GP. If you are not sure which category your place falls into, tell us your suburb and we will tell you what your water actually runs at. Further reading: what happens if you don’t change your water filter, or what chlorine turns into on the way to your tap.