TDS is one of the most familiar numbers in specialty coffee.
You see it on water reports.
You see it on coffee refractometers.
You see brewers discussing 50 ppm, 100 ppm and 150 ppm.
But these numbers don't all mean the same thing.
TDS can refer to the dissolved material in your brewing water.
Or it can refer to the dissolved material in your finished coffee.
Understanding the difference is important.
Because TDS is useful.
But TDS is not the whole story.
What does TDS mean?
TDS stands for Total Dissolved Solids.
In simple terms, it describes the amount of dissolved material present in a liquid.
For brewing water, those dissolved materials can include minerals and ions such as calcium, magnesium, sodium, potassium, bicarbonate, chloride and sulfate.
But there is an important technical point.
A handheld "TDS meter" generally isn't directly measuring every dissolved solid individually.
Most portable TDS meters actually measure electrical conductivity and then convert that conductivity into an estimated TDS value using a conversion factor.
So when your meter says:
60 ppm
it isn't literally counting 60 milligrams of dissolved solids.
It is giving you an estimate based on conductivity.
TDS is an estimate, not a mineral analysis
Different ions conduct electricity differently.
Different meters can also use different conversion factors.
That means the number isn't completely meaningful without knowing how it was measured.
If someone tells you:
"My water is 100 ppm."
the next question should be:
100 ppm measured how?
Water TDS and coffee TDS are different
Before brewing:
Water → TDS
This tells you roughly how much dissolved material is already present in your brewing water.
After brewing:
Coffee + Water → Brewed coffee → TDS
Now the dissolved material is primarily coffee-derived material that has entered the beverage.
A refractometer can estimate the concentration of dissolved coffee solids in the finished brew.
These are completely different measurements.
Why coffee TDS matters
Coffee beverage TDS is related to brew strength.
If more coffee material is dissolved into the same amount of water, the beverage generally becomes more concentrated.
But TDS doesn't tell you everything about the cup.
Two coffees can have the same measured TDS and still taste completely different.
They can differ in acidity, sweetness, bitterness, aroma and mouthfeel.
TDS tells us how much dissolved material is present.
It doesn't tell us which compounds are present.
The same problem exists with brewing water
Imagine two waters.
Water A:
60 ppm TDS
Mostly Mg²⁺ + HCO₃⁻
Water B:
60 ppm TDS
Mostly Na⁺ + Cl⁻
Same approximate number.
Very different chemistry.
That is why we don't want to design coffee water by chasing a TDS number alone.
TDS doesn't tell you alkalinity
Two waters can have the same TDS while having very different buffering behaviour.
TDS is not alkalinity.
TDS is not hardness.
TDS is not a mineral profile.
These measurements describe different aspects of water.
Why do coffee people care about TDS?
Because it is still extremely useful.
TDS gives us a simple number that can help monitor consistency.
It can help identify:
- changes in incoming water
- changes after filtration
- changes after mineralisation
- consistency between batches
- unexpected dilution
- equipment or water-treatment problems
The number is useful as a checkpoint.
TDS and temperature
Electrical conductivity changes with temperature.
That's why many TDS meters automatically compensate for temperature.
When comparing readings, consistent measurement conditions matter.
Otherwise you can end up chasing a number that changed because of temperature rather than because the water itself changed.
Don't confuse water TDS with extraction yield
A coffee beverage might have:
1.40% TDS
But that doesn't directly mean:
14% extraction.
Extraction yield depends on the amount of coffee dissolved relative to the original coffee mass and brew ratio.
TDS and extraction yield are related, but they are different measurements.
TDS is a checkpoint
Don't think:
"My water needs to be 60 ppm because 60 ppm is the perfect coffee water."
Instead:
"My target profile should produce approximately 60 ppm, and TDS gives me a quick way to check whether I am roughly where I expect to be."
The number becomes a quality-control tool rather than the entire recipe.
The number is not the recipe
If someone tells you:
"Use 70 ppm water for specialty coffee."
our next question should be:
70 ppm of what?
Because 70 ppm is a concentration.
It isn't a flavour profile.
It isn't an extraction mechanism.
And it isn't automatically a recipe.
The composition gives the number meaning.
The Water Artist approach
We like TDS.
We use TDS.
But we don't worship TDS.
Our approach is:
Composition first.
TDS second.
First understand what ions are in the water.
Then understand hardness and alkalinity.
Then use TDS as a practical measurement to check consistency.
Ion profile → target water → TDS checkpoint → brew → taste.
Not:
TDS number → assume good water.
TDS is a window, not the whole landscape
TDS gives us a convenient way to look at dissolved material.
But to understand why a water behaves differently, we need to look beyond the number.
We need chemistry.
We need controlled brewing.
And, ultimately, we need the cup.
The Water Artist
Use TDS as a checkpoint, not as the recipe.
Because the question isn't simply:
How much is in the water?
It's:
What is in the water — and what happens when it meets the coffee?
Water is the canvas.
You're the artist.