What Is TDS in Water?
Why a TDS Meter Reading Isn't a Safety Score
TDS, or total dissolved solids, is everything dissolved in your water added together, mostly calcium, magnesium, sodium and other minerals and salts, measured in mg/L (the same as PPM). It's a useful clue to taste and scale, but it can't tell you whether chlorine, fluoride or lead are in your glass. Here's what your TDS meter is really reading, what the numbers mean in Australia, and how to judge a filter properly. For the bigger picture on choosing one, see our best water filter in Australia guide.
Trinity Benchtop Water Filter
Judged by lab results, not a TDS meter
In third-party testing by AS Enviro (ISO/IEC 17025 accredited), Trinity reduced fluoride by 99.5%, chlorine by more than 99.9%, chloramine by 99.0% and lead by more than 99.9%. Then it adds calcium and magnesium back for a smoother taste. No plumbing, no power.
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TDS is the total amount of minerals and salts dissolved in water, in mg/L. The Australian Drinking Water Guidelines (ADWG) treat it as a taste measure: up to 600 mg/L tastes good, and no health limit is set. A TDS meter estimates it from electrical conductivity, so it can't see chlorine, chloramine, fluoride, lead or bacteria in any meaningful way.
To know what a filter removes, look at its lab results. Trinity's AS Enviro report shows 99.5% fluoride, more than 99.9% chlorine and 99.0% chloramine reduction, while its mineral stage keeps the calcium and magnesium your meter counts.
Where the numbers come from: taste bands, the health statement and EC conversion factors are from the NHMRC's ADWG fact sheet on total dissolved solids and SA Health's salinity guidance. City figures are the ones published in our city guides from each utility's reports; they vary by suburb, season and source blend. Trinity figures are from AS Enviro's third-party test report.
What TDS Actually Is
TDS is the weight of everything left behind if you evaporated a litre of water to dryness. In tap water that's mostly harmless minerals and salts picked up from rock, soil and rivers on the way to your dam or bore. Labs measure it that way; your handheld meter estimates it.
The hardness minerals. They give water body and taste, and they're what builds scale on your kettle and shower screen.
Natural salts. River water that's travelled a long way, like the Murray, carries more of them.
Dissolved from limestone and other rock. Bicarbonate helps buffer pH.
Disinfectant residuals, fluoride and trace metals are in there too, but in such small amounts they barely move the total.
That last card is the whole story. TDS is dominated by minerals, so it tells you how mineral-rich your water is, not how clean it is. If you're new to the units, our water filter glossary explains mg/L, PPM and the rest in plain English.
How a TDS Meter Works
A TDS meter doesn't weigh anything. It measures electrical conductivity (EC), how easily a tiny current passes through the water, then multiplies it by a conversion factor to estimate TDS in PPM. Dissolved minerals carry a charge, so more minerals means higher conductivity and a higher reading.
| Step | What happens | Why it matters |
|---|---|---|
| 1. Measure EC | Two probes read conductivity in µS/cm | Only charged particles (ions) conduct |
| 2. Correct for temperature | Most meters adjust to 25°C | Warm water conducts more and reads higher |
| 3. Convert | EC × a factor of about 0.5 to 0.7 | The right factor depends on the water's chemistry |
| 4. Display PPM | Shown as TDS in PPM (= mg/L) | An estimate, not a lab measurement |
The NHMRC says factors of 0.50 to 0.64 are used across Australia; SA Health uses 0.55 for River Murray water and notes a range of 0.5 to 0.7 depending on the source.
What the Numbers Mean
In Australia TDS is an aesthetic (taste) guideline, not a health one. The ADWG says TDS should not exceed 600 mg/L for good palatability, and the NHMRC says no health effects have been associated specifically with high TDS.
| TDS (mg/L) | ADWG taste rating | What you'll notice |
|---|---|---|
| 0 to 600 | ✓ Good | Where nearly all capital city tap water sits |
| 600 to 900 | ⚠ Fair | A noticeable mineral or salty taste, more scale |
| 900 to 1,200 | ⚠ Poor | Common in some regional bore supplies |
| Above 1,200 | ✗ Unacceptable | Unpalatable for most people |
High TDS is mostly a kitchen and bathroom issue: more scale on taps, kettles and shower screens, and a heavier taste. The NHMRC also notes that water with very high or very low TDS can be corrosive. For how health values and taste values differ across every parameter, read our Australian Drinking Water Guidelines explained guide.
What a TDS Meter Can't See
The things most people filter for are either tiny next to the mineral load or carry no electrical charge, so a TDS meter can't single them out. In a glass reading 300 PPM, 1 mg/L of chlorine is about 0.3% of the number, well inside a cheap meter's margin of error.
| What you care about | Typical level in tap water | Does a TDS meter show it? | How to know instead |
|---|---|---|---|
| Chlorine | Usually 0.2 to 1.0 mg/L at the tap | ✗ Lost in the mineral total | Utility report; Trinity >99.9% in lab testing |
| Chloramine | ADWG limit 3 mg/L | ✗ Lost in the mineral total | Utility report; Trinity 99.0% |
| Fluoride | Utilities target about 0.6 to 1.1 mg/L | ✗ Too small to isolate | Trinity 99.5% (2.0 to 0.01 mg/L) |
| Lead | ADWG limit 0.01 mg/L | ✗ Far below meter resolution | Lab test; Trinity >99.9% |
| THMs | ADWG limit 0.25 mg/L | ✗ Mostly uncharged | Lab test; Trinity up to 99.6% |
| Sediment and microplastics | Varies | ✗ Particles, not dissolved ions | Trinity's ceramic stage physically filters fine particles |
That's why we publish Trinity's full third-party report rather than a TDS meter photo. Read more on what's in the water itself in our guides to chlorine in tap water, fluoride in Australian tap water and heavy metals in tap water.
- A seller dips a TDS meter in your tap water, then in their filtered water, and calls the lower number "pure". A lower reading only means fewer minerals.
- An electrolysis demo turns your tap water brown. The colour comes from the metal electrodes reacting in the water, not from dirt in your supply.
- No lab report. Any filter claim worth trusting comes with third-party results for specific contaminants.
TDS in Australian Cities
TDS in Australia depends almost entirely on where your water comes from. Dam-fed Melbourne and Sydney are very low; Murray-fed Adelaide and groundwater-blended Perth are the highest of the capitals. All of them sit inside the ADWG's 600 mg/L taste guideline.
| City | Typical TDS | Why | City guide |
|---|---|---|---|
| Melbourne | As low as 11 to 38 mg/L (inner suburbs) | Protected forest catchments, soft water | Melbourne tap water → |
| Sydney | About 48 to 80 mg/L | Dam water, soft | Sydney tap water → |
| Brisbane | About 80 mg/L (100 to 180 in some outer zones) | Wivenhoe-fed SEQ grid | Brisbane tap water → |
| Perth | 100 to 576 mg/L (central Perth near the top) | Groundwater, desalination and dam blend | Perth tap water → |
| Adelaide | About 480 mg/L | River Murray salts | Adelaide tap water → |
Figures as published in our city guides from utility reports; they vary by suburb, season and source blend. High-TDS cities also tend to be hard-water cities: see which Australian cities have the hardest water.
Why Filtered Water Can Read the Same
A good drinking water filter targets the things you don't want and keeps the minerals that make water taste like water. So a TDS reading after Trinity can sit close to your tap reading, or even a little higher, while chlorine, chloramine, fluoride and lead have dropped sharply.
| Trinity stage | What it does | Effect on a TDS meter |
|---|---|---|
| Ceramic | Physically filters rust, sediment and fine particles | Little change (particles aren't dissolved) |
| Activated alumina, KDF and carbon blend | Reduces fluoride 99.5%, chlorine >99.9%, chloramine 99.0%, lead >99.9% | Barely visible (these are tiny amounts) |
| Mineral stage | Adds calcium and magnesium back, can raise pH by up to +2.0 | Can nudge the reading up |
Water with almost nothing dissolved in it tastes flat, which is why Trinity puts minerals back rather than stripping everything out. Compare options in our best benchtop water filter guide, or see how filters are judged in do tap water filters work?
Best overallTrinity99.5% fluoride, >99.9% chlorine, 99.0% chloramine; minerals added back. 12, 16 or 22 L.
Plastic-free tank100% Glass TrinitySame lab-tested media in borosilicate glass tanks with a bamboo lid and stand. 8 L.
On the tapTap MateTwists onto your tap in under 60 seconds. Up to 99% chlorine; keeps calcium and magnesium.
Want proof, not a meter reading? Trinity's full AS Enviro report lists every contaminant tested and the measured reduction.
See Trinity →Hydrogen Water and TDS
Dissolved hydrogen is a gas with no electrical charge, so a TDS meter reads hydrogen water the same as the water you started with. Hydrogen is measured in PPM of dissolved H₂, a separate reading from the PPM on a TDS meter. The Hydronizer Classic reaches 2.4 PPM, the Pro 5 PPM and the Infinity 10 PPM in about 3 minutes. Our PPM vs ORP guide explains how to read those numbers, and the best hydrogen water bottle guide compares the range.
How to Use a TDS Meter Properly
A TDS meter is a cheap, handy tool for tracking minerals, taste and scale. Use it for that, and use lab results for safety and filter performance.
Warm water reads higher. Compare cold tap with cold filtered water, ideally in clean glasses.
Rinse the probe between samples and check it now and then against a calibration solution.
A sudden jump in your tap reading can mean a source change. Your utility's report will explain it.
It lists TDS, hardness, sodium, chlorine and fluoride separately, which a meter never can.
The takeaway: TDS tells you how mineral-rich your water is. It doesn't tell you how clean it is. Judge a filter by its lab report, and enjoy the minerals that make water taste good.
FAQ
What is a good TDS level for drinking water?
The Australian Drinking Water Guidelines rate TDS by taste: up to 600 mg/L is good, 600 to 900 mg/L fair, 900 to 1,200 mg/L poor and above 1,200 mg/L unacceptable. Most capital city tap water sits well under 600 mg/L. There is no health-based TDS limit.
Is high TDS water bad for you?
The NHMRC says no health effects have been associated specifically with high TDS. A high reading mostly means more dissolved minerals and salts, which changes the taste and adds to scale on kettles, taps and shower screens. If you're watching your salt intake, your utility's water quality report lists sodium on its own line.
Can a TDS meter tell me if my water is safe to drink?
No. A TDS meter estimates total dissolved minerals from electrical conductivity. It can't identify chlorine, chloramine, fluoride, lead, bacteria or microplastics, because those are either tiny fractions of the total or don't carry an electrical charge. Safety comes from your utility's testing, and filter performance from lab results.
Why does my filtered water show a similar or higher TDS reading?
Because a good filter isn't trying to strip your water bare. Trinity reduces chlorine, chloramine, fluoride and heavy metals, then adds calcium and magnesium back in its mineral stage for a smoother taste. Those minerals register on a TDS meter, so the reading can stay similar or even rise while the water is cleaner.
Does a TDS meter measure hydrogen in hydrogen water?
No. Dissolved hydrogen is a gas with no electrical charge, so it doesn't show up on a TDS or EC meter. Hydrogen water is measured in PPM of dissolved hydrogen with a dedicated reagent or meter, which is how the Hydronizer's 2.4, 5 and 10 PPM figures are quoted.
What is the TDS of Australian tap water?
It depends on the source. The NHMRC notes major city supplies range from under 100 mg/L to over 750 mg/L, with some regional groundwater supplies above 1,000 mg/L. Melbourne and Sydney are very low, Brisbane is low, and Adelaide and parts of Perth are the highest of the capitals.
How do I convert EC to TDS?
Multiply the electrical conductivity in µS/cm by a factor, usually between 0.5 and 0.7. The NHMRC says factors of 0.50 to 0.64 are used across Australia, and SA Health uses 0.55 for River Murray water. Most handheld TDS meters do this conversion for you.
Go Deeper
KDF, catalytic carbon, activated alumina, micron, PPM and 50 more terms in plain English.
Deep dive →What every limit means, and why health and taste values are treated differently.
Buyer's guide →Both Trinity filters compared side by side, with no plumbing needed.
Deep dive →Hardness by city, and what it means for scale, showers and appliances.
Try Trinity risk-free for 100 days.
Lab-tested reductions for fluoride, chlorine, chloramine and lead, with calcium and magnesium added back. Free shipping over $99.
Written by AJ, Founder of HolyH₂O. A self-confessed water nerd who started asking questions about his family's water and never really stopped. Questions? Email hi@holyh2o.com.au.
Australian mains water meets the Australian Drinking Water Guidelines. TDS guidance is from the NHMRC and SA Health. Trinity reduction figures are from third-party testing by AS Enviro, an ISO/IEC 17025:2017 accredited laboratory; results vary with source water and usage. This guide describes water quality and filtration performance and is not medical advice.