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If you want to understand whether your brewing water is affecting your coffee, there's a very simple experiment you can try at home.
Brew the same coffee twice.
Keep the recipe as consistent as possible.
Change only the water.
Then taste the two cups side-by-side.
You may notice a substantial difference. You may notice a subtle one. You might even prefer your usual water.
That's exactly the point.
Don't assume your water is bad. Test it.
Why Compare Brewing Water?
Coffee is mostly water, so the water you use can influence the final cup.
But “good coffee water” isn't simply about whether water tastes clean on its own.
Dissolved minerals, alkalinity, hardness and treatment can all affect brewing and flavour.
Water also varies considerably from one location to another.
That means advice such as:
“UK tap water is too hard for coffee.”
is far too broad.
Some areas have relatively hard water. Others have considerably softer water. Household treatment and filtration can change things further.
The easiest first step isn't to guess what's coming from your tap.
It's to compare it.
The Simple Water Comparison Test
What You'll Need
- The same coffee beans
- Your usual brewer
- Your grinder
- Scales
- Your normal tap or filtered water
- A second water suitable for drinking
- Two cups
The second water doesn't need to be treated as the “correct” water.
It's simply your comparison.
If you use bottled water, check the label and choose something reasonably neutral rather than assuming a particular brand will automatically improve your coffee.
Step 1: Establish Your Recipe
Use a recipe you already know reasonably well.
Record:
- Coffee dose
- Water quantity
- Grind setting
- Water temperature, if measured
- Brewing method
- Basic pouring or steeping technique
- Brew time
The aim is to make two brews that are as similar as reasonably possible apart from the water.
Step 2: Brew Cup A
Brew your normal recipe using your usual water.
Don't deliberately change anything because you expect this cup to be worse.
Use the same care you normally would.
Label it Cup A.
Step 3: Brew Cup B
Repeat the recipe using your comparison water.
Keep the following stable:
- Coffee
- Dose
- Water quantity
- Grind
- Temperature
- Brewing technique
Label this one Cup B.
Step 4: Let Both Coffees Cool a Little
Don't rush the tasting while the coffee is extremely hot.
As coffee cools, flavour differences can become easier to notice.
Taste the cups several times rather than making a decision from the first sip.
Step 5: Compare Without Looking for a “Winner”
Go back and forth between Cup A and Cup B.
Ask:
- Does one seem sweeter?
- Is the acidity different?
- Does one taste cleaner or more muddled?
- Is there a difference in bitterness or dryness?
- Does the body feel different?
- Can you distinguish flavours more easily in one?
- Does one have a more enjoyable finish?
- Which cup do you actually prefer?
There is no requirement for Cup B to win.
Your normal water might perform perfectly well with that coffee and recipe.
Make the Test Better: Taste It Blind
If somebody else is available, ask them to swap the cups around without telling you which is which.
Then taste again.
This removes some expectation from the experiment.
If you already know that one cup contains the “special” water, it's very easy to start looking for reasons why that cup should taste better.
A simple blind comparison makes the exercise much more useful.
What If the Coffees Taste Different?
That's useful information — but don't jump immediately to a conclusion.
You have established that changing the water appears to change the cup.
You haven't necessarily established why.
Several characteristics of water can matter.
Hardness
Water hardness is associated mainly with dissolved calcium and magnesium.
These minerals are relevant both to brewing behaviour and to scale formation inside equipment.
Alkalinity
Alkalinity describes the water's ability to resist changes in acidity.
In coffee brewing, different alkalinity levels can affect how acidity is perceived in the finished drink.
Chlorine and Treatment
Depending on the local water supply and household setup, treatment-related tastes or odours may also affect the sensory result.
Overall Mineral Composition
A single TDS reading doesn't tell you the complete mineral composition of water.
Two waters can have similar total dissolved solids while containing different amounts and types of dissolved minerals.
So avoid treating one TDS number as a universal target for good coffee.
What If You Can't Taste Much Difference?
That's also a perfectly useful result.
It might mean your normal water works well with the coffee you're brewing.
The difference might also be too small to matter to you.
And that's important.
You don't need to create a water problem simply because coffee enthusiasts discuss water chemistry.
If you're happy with your coffee and a controlled comparison doesn't reveal a meaningful improvement, there may be more useful brewing variables for you to investigate.
Don't Assume Bottled Water Is Automatically Better
“Bottled water” isn't one type of water.
Different bottled waters have different mineral compositions.
Some may work nicely for a particular coffee or brewing method. Others may not.
Packaging and mineral composition can also change over time, so it's better to check the current label than rely indefinitely on an old internet recommendation.
The purpose of this experiment is therefore not:
Tap water versus perfect bottled water.
It's:
Water A versus Water B.
If you prefer B, you've found something worth investigating further.
Should You Use Filtered Water?
A household water filter can change the characteristics of your tap water, but different filtration systems do different jobs.
Some are primarily designed to improve taste and reduce substances such as chlorine. Others may also affect hardness or mineral content.
Rather than assuming that any filter will “fix” coffee water, repeat the same comparison:
Tap water → filtered water → taste side-by-side.
If the filtered cup consistently tastes better to you, that's useful evidence.
Follow the filter manufacturer's instructions for cartridge replacement and use.
Should You Make Your Own Brewing Water?
Some coffee enthusiasts use low-mineral or purified water and add measured minerals to create repeatable brewing water.
This can be an interesting way to explore water chemistry, particularly if you want greater control over your brewing experiments.
But it isn't necessary for everybody.
And there isn't one DIY mineral recipe that is automatically ideal for every coffee, brewer and preference.
If you explore remineralised water, treat the mineral composition as another brewing variable rather than a recipe that guarantees better coffee.
Important: Don't use distilled or reverse-osmosis water in an espresso machine unless the resulting water meets the machine manufacturer's water requirements. Water chemistry can affect scale, corrosion and machine operation, and requirements vary by manufacturer.
Can You Use the Test With Espresso?
In principle, water can be compared with espresso too — but there's an important practical difference.
With a pour-over brewer, changing water is easy.
With an espresso machine, the water sits inside tanks, pipes, boilers or thermoblocks depending on the design.
Simply pouring different water into the reservoir doesn't necessarily mean the next shot is brewed exclusively with that water.
More importantly, you should use water compatible with the manufacturer's requirements.
So for this simple home experiment, manual brewing is the easier and more controlled place to start.
Try the Test With More Than One Coffee
If the first comparison is interesting, repeat it with another coffee.
For example:
- A lighter roast
- A more developed roast
- A washed coffee
- A naturally processed coffee
- A coffee from another origin
You may discover that the water difference is more noticeable with some coffees than others.
That's more useful than trying to prove that one water is universally “best”.
Record What You Notice
A very simple tasting note is enough.
| Characteristic | Cup A | Cup B |
|---|---|---|
| Sweetness | Notes | Notes |
| Acidity | Notes | Notes |
| Bitterness | Notes | Notes |
| Clarity | Notes | Notes |
| Body | Notes | Notes |
| Overall preference | Notes | Notes |
You don't need to identify blueberry, jasmine, caramel or any other specific tasting note.
“A is sweeter, B is more drying, I prefer A” is perfectly useful information.
Water, Grind and Temperature Work Together
One reason water chemistry can become confusing is that it doesn't operate independently from the rest of the recipe.
Your cup is influenced by a combination of:
- Coffee
- Water
- Grind
- Ratio
- Temperature
- Contact time
- Agitation
- Brewing technique
That's why our approach across these guides is:
CHANGE ONE THING → BREW AGAIN → COMPARE
If you're investigating water, keep the other major variables stable.
If you're investigating temperature, keep the water stable.
That way each experiment teaches you something.
Go Further With Your Brewing Experiments
Pour-Over Perfection — 2026 Premium Edition is our practical guide to understanding V60, Chemex, Kalita Wave, AeroPress and Clever Dripper brewing.
Explore water, grind, temperature, ratio, agitation and pouring technique through practical experiments, troubleshooting tools and reusable worksheets.
The approach throughout the guide is:
BREW → TASTE → DESCRIBE → ADJUST → COMPARE → RECORD
Explore Pour-Over Perfection →
What Should You Do If Water Makes a Big Difference?
If you repeatedly prefer one water in controlled comparisons, you have several options.
- Keep using your existing water if you're happy with it.
- Try household filtration and compare the result.
- Investigate your local water using information from your water supplier.
- Compare other drinking waters rather than assuming the first alternative is optimal.
- Explore controlled remineralisation if you want to experiment more deeply.
The goal isn't to create the theoretically perfect water.
It's to understand whether water is materially affecting your coffee and decide whether changing it is worthwhile.
The Real 5-Minute Lesson
The most valuable part of this test isn't discovering that bottled water beats tap water.
It might not.
The useful lesson is discovering that you can isolate a brewing variable and taste what happens when you change it.
That's a skill you can use everywhere:
Water today.
Grind tomorrow.
Temperature next time.
Ratio after that.
Instead of memorising somebody else's perfect recipe, you gradually learn how your own coffee responds.
Final Thoughts
Water can make a meaningful difference to coffee, but don't let somebody else's postcode, mineral target or bottled-water preference decide what's in your kettle.
Run the experiment.
Keep the recipe consistent.
Taste the coffees side-by-side.
Ideally, taste them without knowing which is which.
Then ask the only question that matters at this stage:
Can I taste a difference — and which do I prefer?
That's a much better starting point for understanding coffee water than assuming yours needs fixing.
Related Coffee Guides
- Why UK Water Chemistry Matters for Coffee — understand hardness, alkalinity and how your local water can affect brewing.
- Coffee Brewing Temperature: Does 93°C Really Matter? — learn how temperature interacts with your brewing water and recipe.
- The Coffee Compass: How to Troubleshoot Pour-Over Coffee — use a controlled process to diagnose brewing problems.
- 5 Grind Mistakes That Make Your Coffee Taste Sour or Bitter — understand when changing grind is actually useful.
Want the Complete Coffee Learning Path?
The Advanced Home Barista Collection brings together Pour-Over Perfection, Coffee Tasting & Cupping and Home Barista Masterclass in one practical collection covering manual brewing, sensory development, espresso, milk and latte art.
Each guide combines detailed learning with practical exercises, troubleshooting tools and reusable reference material designed to help you keep improving at home.