One of the simplest ways to understand coffee water is to stop talking about it and test it.
Take one coffee.
Prepare four waters.
Keep everything else constant.
Then taste.
This experiment is designed to isolate the effect of water as much as possible.
The objective
The question is simple:
Does changing water composition change the sensory expression of the same coffee?
We are not trying to prove a universal rule.
We are testing one coffee under controlled conditions.
Keep the coffee constant
Use one coffee for all four brews.
Record:
origin
processing
roast date
roast level
dose
grind setting
and storage conditions.
Use the same batch of coffee throughout the experiment.
Keep the recipe constant
Choose one brewing recipe.
For example:
15 g coffee
250 g water
93°C
fixed pouring structure
fixed brew time target
The exact recipe is less important than consistency.
Four water profiles
Water A — Low mineral
A relatively low-mineral baseline.
Purpose:
Establish a reference point.
Water B — Magnesium-forward
Increase magnesium while keeping other variables as controlled as practical.
Purpose:
Explore a magnesium-forward direction.
Water C — Calcium-forward
Increase calcium while maintaining a comparable overall mineralisation where practical.
Purpose:
Explore a calcium-forward direction.
Water D — Higher alkalinity
Increase buffering while keeping other parameters reasonably controlled.
Purpose:
Observe how acidity and balance respond.
Measure the water
Record:
TDS
calcium
magnesium
alkalinity
and the salts used.
Don't rely on TDS alone.
Blind the samples
If possible, label the cups:
A
B
C
D
without revealing the water profiles.
Taste first.
Reveal the profiles afterward.
This reduces expectation bias.
What should you evaluate?
Score:
aroma
acidity
sweetness
body
clarity
bitterness
finish
balance
overall preference
Don't assume what each water should taste like.
Write what you actually perceive.
What would count as a useful result?
Suppose Water B consistently produces a cup you prefer.
That's useful.
But the result only tells you:
"This coffee responded positively to this water under these brewing conditions."
It does not prove:
"Magnesium always makes coffee better."
That's an important distinction.
Repeat the experiment
If possible, repeat the experiment on another day.
If the same pattern appears, confidence increases.
Then test another coffee.
Now you can start asking whether the response is coffee-specific or more general.
The next experiment
Once you identify a preferred water, change only one part of the profile.
For example:
same magnesium
different chloride/sulfate ratio
or:
same hardness
different alkalinity.
This moves the experiment from broad comparison to more precise formulation.
The Water Artist
Good water experiments don't try to prove a theory immediately.
They create better questions.
Taste first.
Measure second.
Hypothesise third.
Then test again.
Water is the canvas.
You're the artist.