Imagine two bottles.
Both say:
60 ppm TDS.
Are they the same water?
No.
They may have similar dissolved material according to the meter.
But the ionic composition can be very different.
Build two waters
For this experiment, create:
Water A — magnesium-forward
Water B — calcium-forward
Adjust the total mineralisation so that both produce a similar TDS reading.
The exact formulation depends on the salts and measurement system.
The important point is that the TDS should be similar while the composition differs.
Why do this?
Because it demonstrates one of the biggest limitations of TDS.
The number doesn't tell you the composition.
Keep the coffee constant
Use:
one coffee
one grinder
one dose
one ratio
one temperature
one brewer
one recipe.
Only the water changes.
Taste blind
Don't tell yourself which water is which.
Taste the cups first.
Write notes.
Then reveal the profiles.
What might happen?
Perhaps one cup feels brighter.
Perhaps one feels rounder.
Perhaps the difference is tiny.
Perhaps there is no meaningful difference for that coffee.
All three outcomes are useful.
A controlled experiment doesn't need to produce the result you expected.
Repeat
Repeat the experiment.
Then use another coffee.
This is important because a single coffee can produce a single response.
The result is not necessarily universal.
What if the TDS meters disagree?
That's possible.
Different meters can use different conversion factors.
Temperature and measurement technique also matter.
So if the experiment depends on matching TDS, use the same meter and procedure for both waters.
The deeper lesson
The experiment isn't really about 60 ppm.
It is about composition.
The TDS number is a convenient summary.
The chemistry underneath it is the interesting part.
The Water Artist
When someone says:
"My water is 60 ppm."
our next question is:
"60 ppm of what?"
Because the number alone isn't the water.
Water is the canvas.
You're the artist.