Australian Tap Water TDS by City and Suburb: Find Your Local Reading

Water spots after a wash come down to one number: the Total Dissolved Solids (TDS) in your tap water. The minerals behind that number are completely natural and perfectly fine to drink. They only become a nuisance when water dries on paint, glass or solar panels and leaves them behind as white spots.

This guide is the most complete public collection of Australian tap water TDS figures we know of: 278 cities, towns and supply zones, compiled from the latest annual drinking water quality reports of more than 40 Australian water authorities. Australia's spread is enormous. Cairns sits near 25 ppm, Melbourne around 50 ppm, most of Sydney between 90 and 145 ppm, Perth's northern suburbs near 576 ppm and Geraldton at 854 ppm. The right DI tank setup depends on where you sit in that range, and the payoff is the same everywhere: purified water that dries without spots. Wash. Rinse. Pack up.

Last updated August 2026. Figures come from each authority's most recent published report; the data year is shown for every row.

What Is My TDS? Look Up Your Suburb

Your TDS is the amount of dissolved mineral in your tap water, measured in parts per million (ppm). In Australia it ranges from about 25 ppm in Cairns to more than 850 ppm in Geraldton, and it can differ between suburbs of the same city. Type your suburb or town below to see your local figure, what it means for water spots, and a resin life guide for your water.

What Is TDS and Why Does It Matter for Car Washing?

TDS stands for Total Dissolved Solids. It is a measurement (in parts per million, or ppm, which is the same as mg/L) of everything dissolved in your water: calcium, magnesium, sodium, chloride, bicarbonate, sulfate, silica and more. When you rinse your car with tap water and let it dry, those dissolved minerals stay behind on your paint, glass and trim as white spots and streaks.

The higher your TDS, the more mineral is in every drop. At 50 ppm the spots are light. At 250 ppm they are obvious. Above 500 ppm they are severe, and mineral deposits left to bake in the sun can etch into clear coat.

A DI (deionised) water tank strips these dissolved minerals out by passing your tap water through ion exchange resin. With fresh resin the output reads 0 ppm on a TDS meter, and water that pure dries clean with no spots and no drying needed.

TDS vs Water Hardness: They Are Not the Same Thing

Many Australian water authorities publish water hardness, not TDS. Hardness measures only calcium and magnesium (the minerals behind limescale). TDS measures everything dissolved in the water, so it is always higher than hardness, often two to three times higher. Brisbane's published hardness is about 115 mg/L, while the blended grid's reported TDS average is around 300 mg/L. If the only figure you can find is labelled hardness, do not treat it as your TDS. A $15 TDS meter gives you the true number in seconds, and every Spot Free Rinse tank includes one free.

Is My Water Hard or Soft?

As a quick rule of thumb using TDS: under 100 ppm is soft (Melbourne, Hobart, Cairns, Canberra, Wollongong), 100 to 200 ppm is moderately soft (most of Sydney, Newcastle, the Central Coast, Darwin, Mandurah), 200 to 400 ppm is moderately hard (Brisbane's south side, Adelaide on an average blend, much of regional Queensland), and above 400 ppm is hard (most of Perth, Kalgoorlie, the WA Wheatbelt and Mid West). Hard water is completely normal and fine to drink; the minerals simply show up as spots when the water dries on paint, glass or panels.

Australian Tap Water TDS: The National Picture

Reticulated tap water in Australia spans more than a 50x range, from about 25 ppm in Cairns to over 1,300 ppm at Horrocks on the WA coast. The National Health and Medical Research Council's Australian Drinking Water Guidelines treat TDS up to 600 ppm as good from a taste perspective, and plenty of perfectly healthy supplies sit above that. For spot free rinsing, the number simply tells you how hard your resin will work and which tank size gives the best value.

Capital cities at a glance

The softest reticulated water in Australia

Cairns (about 25 ppm), Frankland WA (40), Cranbrook WA (45), Swan Hill (about 45), Hobart (about 49), Melbourne (about 50), Jerramungup WA (57), Gloucester NSW (66), Grafton (66), Canberra (77) and Lismore (83). If you live in one of these areas, a Medium 10L tank will run for a very long time between resin changes.

The most mineral rich reticulated water in Australia

Horrocks WA (1,305 ppm), Nanango QLD (about 1,200), Guilderton WA (1,118), New Norcia WA (992), Jurien Bay WA (991), Halls Creek WA (974), Cervantes WA (972), Marble Bar WA (965), Northampton WA (887), Mullewa WA (884), Dongara WA (880), Yuna WA (870), Nabawa WA (865), Geraldton WA (854). These are mostly groundwater supplies, and they are exactly where a Large or XL tank, ideally with an RO pre-filter, earns its keep.

TDS by State and Town

Every figure below comes from the named authority's own published data, with the reporting year shown. Where an authority publishes conductivity instead of TDS, the estimate uses the standard conversion (TDS is roughly 0.6 times conductivity in uS/cm) and the note says so. Supplies do vary with season and source blend, so treat these as a reliable guide and your own TDS meter reading as the final word.

Queensland

South East Queensland is a blended grid, so the same suburb can swing with which treatment plant is supplying it. South of the Brisbane River (Mt Crosby supply) runs noticeably higher than the north side (North Pine supply).

New South Wales and ACT

Sydney Water publishes typical TDS for each of its twelve delivery systems every quarter, so Sydney has some of the best public data in the country. Regional NSW councils vary widely in what they publish.

Victoria

Melbourne has some of the softest tap water of any major city in the world thanks to protected mountain catchments. Most Victorian utilities publish conductivity rather than TDS, so several figures below are estimated from conductivity.

Tasmania

Tasmanian water is generally very soft. TasWater publishes per-address data through its online water quality portal rather than in a single table.

South Australia

SA Water no longer publishes a per-town TDS table. Adelaide's TDS moves with the blend of reservoir, River Murray and desalinated water, which is why the official range is wide. For your exact street, use SA Water's online drinking water profile tool.

Northern Territory

Power and Water publishes TDS in its annual drinking water quality report. Darwin is moderate; Alice Springs groundwater is the highest of the major centres.

Western Australia

Water Corporation publishes suburb-zone TDS tables for Perth and every regional scheme, which makes WA the best documented state, and also the one with the widest spread: from about 40 ppm at Frankland to over 1,300 ppm at Horrocks.

Bore Water, Tank Water and Dam Water

If you are not on mains supply, your TDS can be very different from the figures above. Domestic bore water in Australia typically ranges from 300 to 1,500 ppm, and some Western Australian bores exceed 5,000 ppm. Rainwater tank water is usually very low, around 10 to 30 ppm off a clean roof. Dam water varies with catchment geology. Whatever your source, the free TDS meter included with every Spot Free Rinse tank tells you exactly what you are working with.

How to Test Your Water

A TDS meter is a small pen sized device that gives an instant reading in ppm. Dip it in a glass of your tap water and read the number. Every Spot Free Rinse DI tank includes a free TDS meter so you can:

1. Test your tap water to know your input TDS
2. Test the output from your DI tank to confirm it is reading 0 ppm while the resin is fresh
3. Watch for the output starting to climb, which tells you the resin is due for replacement

Readings shift with season and source blending. Authorities mix reservoir, river, bore and desalinated water depending on demand, so your TDS can be lower in winter and higher in summer. Testing a few times across the year gives you your real range.

How TDS Affects DI Resin Life

DI resin exchanges its hydrogen and hydroxide ions for the dissolved minerals in your water. The more minerals in your supply, the more work the resin does on every rinse. Your local TDS is the single biggest factor in how many litres of purified water a tank produces, which is why matching tank size to your area is worth getting right.

The relationship is simple: resin capacity is used in proportion to the mineral it removes. A tank in Melbourne or Hobart at around 50 ppm lasts roughly six times as long between refills as the same tank on 300 ppm water, which is why soft water customers rave about how rarely they touch the resin. In mineral rich areas the tank works harder, and the answer is simply more resin: stepping up to a 15L or 25L tank means more washes per fill and a lower cost per wash, with identical spot free results. Above about 500 ppm, pairing the tank with an RO (reverse osmosis) pre-filter changes the economics completely, because the RO removes 90 to 95 percent of minerals before the water ever touches the resin.

Use the resin life calculator for a precise estimate for your water and vehicle, and see the tank sizing guide for a full walkthrough.

Choosing the Right DI Tank for Your Water

Under 100 ppm, a Medium 10L tank lasts a very long time and is all most people need. Between 100 and 300 ppm the Medium is still the most popular pick, with the Large 15L making sense for frequent washers or multiple vehicles. Above 300 ppm the Large or XL 25L gives you more washes per fill and a lower cost per wash, with identical spot free results.

Ready to see the numbers for your water? Visit the product page, enter your TDS into the calculator, and compare tank sizes. Every tank ships with a free TDS meter so you can confirm your reading on day one.

Where These Figures Come From

Every number on this page is drawn from the named water authority's own published documents: annual drinking water quality reports, quarterly quality reports and typical composition tables. Where an authority publishes only conductivity, the TDS estimate uses the standard 0.6 conversion and is flagged in the notes. Where an authority publishes no TDS at all (a surprising number only publish hardness), we say so rather than guessing. Figures are updated as authorities release new reports.

Frequently Asked Questions

What is TDS in water?

TDS (Total Dissolved Solids) is a measure of all the dissolved minerals, salts and metals in water, expressed in parts per million (ppm) or milligrams per litre (mg/L); the two units are interchangeable. These dissolved minerals are what cause water spots on cars, glass and solar panels when water dries on the surface.

What is a good TDS level for tap water in Australia?

For drinking, the Australian Drinking Water Guidelines describe TDS up to 600 ppm as good from a taste perspective, and TDS is treated as an aesthetic measure rather than a health one, so a high reading does not mean unsafe water. For spot free rinsing the maths is simpler: the lower your TDS, the fewer minerals dry onto the surface, and purified water at 0 ppm leaves none at all.

What does my TDS meter reading mean?

Under 100 ppm: soft water, light spotting, excellent resin life. 100 to 200 ppm: moderate, visible spots when water dries in the sun. 200 to 400 ppm: mineral rich, spots form quickly. Over 400 ppm: expect heavy spotting and consider a larger tank or an RO pre-filter. And if you are reading the output of a DI tank, fresh resin should read 0 ppm; a climbing reading means the resin is nearing replacement.

What TDS level causes water spots on cars?

Any TDS above 0 can leave spots. They become noticeable above about 50 ppm and a real nuisance above 150 ppm, sooner on dark or metallic paint. For a truly spot free result you want purified water reading 0 ppm on a meter, which is what a DI tank with fresh resin produces.

Which Australian city has the hardest water?

Among the capitals, Perth's northern suburbs have the highest reticulated TDS, with the Yanchep and Neerabup zones averaging around 572 to 576 ppm in Water Corporation's 2024-25 data, due to Gnangara Mound groundwater. Among all sizeable Australian towns, Geraldton at 854 ppm and a band of Mid West WA towns above 800 ppm top the list, with Horrocks the highest scheme average at about 1,305 ppm.

Which Australian city has the softest water?

Cairns has the softest tap water of any Australian city at about 25 ppm, from rainforest catchments. Among the capitals, Hobart (about 49 ppm) and Melbourne (about 50 ppm) are the softest, followed by Canberra at about 77 ppm.

Is Australian tap water hard or soft?

Both, depending entirely on where you live. Melbourne, Hobart, Cairns and Canberra are very soft (under 80 ppm). Sydney runs 88 to 144 ppm depending on delivery system. Brisbane's blended grid averages around 300 ppm, with the north side softer than the south. Adelaide ranges 150 to 400 ppm with the source blend, and Perth spans 129 to 576 ppm depending on suburb.

Why does Brisbane's south side spot worse than the north side?

Different treatment plants. The south side (including Pallara, Sunnybank, Annerley and Ipswich) is mostly supplied from the Mt Crosby plants on the Brisbane River, whose catchment geology contributes more minerals; meter readings of 180 to 300 ppm are common. The north side is mostly supplied from North Pine, which runs much lower, typically 90 to 160 ppm. Because the SEQ grid blends sources, your reading can shift week to week.

Why is Perth water TDS so different from suburb to suburb?

Perth draws on three very different sources: groundwater from the Gnangara and Jandakot mounds (filtered through limestone, so mineral rich), hills dam water (low TDS) and desalinated seawater (very low TDS, remineralised for taste). Northern suburbs get the most groundwater and read highest, around 458 to 576 ppm. Suburbs fed mainly by desalination, like the Rockingham area at about 129 ppm, read lowest. That is a 4x spread within one city.

Does my local water quality affect how fast DI resin runs out?

Yes, it is the single biggest factor. Resin capacity is consumed in proportion to the minerals it removes, so a tank on 50 ppm Melbourne water lasts roughly six times as long as the same tank on 300 ppm water and roughly ten times as long as on 500 ppm water. That is why the same 10L tank suits a Melbourne driveway perfectly and why Perth and Wheatbelt customers get better value from a 15L or 25L.

Does water quality change by season in Australia?

Yes, particularly where authorities blend sources. Adelaide is the clearest example: more River Murray water in the blend pushes TDS toward the top of the official 150 to 400 range, while reservoir and desalinated supply pulls it down. Brisbane's grid, Sydney's systems and Perth's zones all shift too, which is why the tables above show ranges as well as typical figures.

Is rainwater already spot free?

Close to it. Clean tank rainwater usually reads 10 to 30 ppm, low enough that most people see few spots. Roof dust and debris can push it higher. If your tank water reads under 10 ppm, you may not need purification at all; the meter will tell you.

Does bore water cause more water spots than tap water?

Usually, and often dramatically. Australian bore water commonly runs 300 to 1,500 ppm, and some WA bores exceed 5,000 ppm. If you wash with bore water, a DI tank (with an RO pre-filter for the highest readings) is the difference between constant spotting and a clean dry finish.

What TDS is too high for a DI tank?

There is no hard cutoff: a DI tank produces purified water at any input TDS. The question is economics. Above about 500 ppm the resin works so hard that pairing the tank with an RO pre-filter, which knocks out 90 to 95 percent of minerals first, gives far more litres per resin fill and the lowest cost per wash. That is the setup we recommend for Geraldton, Karratha, the Mid West coast and high TDS bores.

Where do these TDS figures come from?

From the published water quality reports of more than 40 Australian water authorities, listed in full in the source list above, with the reporting year shown for every location. Where a utility publishes conductivity instead of TDS the note on that row says the figure is an estimate. Supplies vary with season, so use your own TDS meter reading as the final word.