Water for coffee – how hardness, minerals and limescale affect the taste
Water is one of the ingredients that has the greatest impact on your coffee – but also one of the easiest to overlook.
You can use good coffee beans, the right grind size and a precise recipe, but if the water is not well-suited for brewing coffee, the result can still be different from what you expect.
This does not mean that you need to become an expert in water chemistry to make good coffee.
For most people, it is primarily about understanding a few things:
- water hardness
- mineral content
- alkalinity
- any taste or odor from the water
- the risk of limescale in the coffee machine.
In this guide, we review how water affects both the taste of your coffee and your coffee equipment, and when it might be worth trying filtered water.
Quick answer: What water is best for coffee?
Good brewing water should, first and foremost:
- taste and smell clean
- contain minerals
- not be extremely hard
- not be completely devoid of minerals
- have a composition that is suitable for both coffee and brewing equipment.
Ordinary tap water can therefore easily work well for coffee.
If your water is very hard, has a distinct taste of chlorine or causes major limescale problems, filtration or other water treatment may be worth investigating.
The most important thing is to understand that the water that is best for the taste of the coffee must also be suitable for the equipment you are brewing with.
Why does water mean so much for coffee?
A cup of filter coffee consists mainly of water.
At the same time, water is the solvent that extracts various compounds from the ground coffee during brewing.
This means that the composition of the water can affect:
- how much is extracted from the coffee
- how the acidity of the coffee is perceived
- the balance of the taste
- how clearly different aromas appear.
Water therefore plays an active role in the brewing process.
It is not just something that makes the coffee liquid.
If you are already working with dosage and grind size, water is a natural next area to explore.
You can also read our guide to grind size and our guide to coffee dosage.
What does water hardness mean?
When we talk about hard or soft water, it is mainly about the amount of dissolved calcium and magnesium ions.
Water with a lot of calcium and magnesium is referred to as harder water.
Water with less is referred to as softer.
The minerals are important for coffee brewing because water with different mineral compositions can extract and highlight the coffee's flavor compounds differently.
However, hardness also matters for the coffee machine.
Part of the minerals in hard water can form limescale deposits when heated.
This means that water must be assessed from two sides:
How does it affect the taste of the coffee?
and
How does it affect the coffee machine?
Is hard water bad for coffee?
Not necessarily.
Minerals in water are not a problem in themselves. On the contrary, minerals play an important role in coffee brewing.
The problem arises if the composition of the water is so hard or alkaline that it affects the taste of the coffee or causes major limescale problems in the equipment.
Very hard water can, among other things, be less practical in espresso machines and coffee machines, because more limescale can form.
However, this does not mean that the solution is always to remove all minerals from the water.
The goal is balance.
What is alkalinity?
Alkalinity describes the water's ability to neutralize acid.
It is particularly interesting in coffee because coffee naturally contains various acids.
If the water has high alkalinity, it can neutralize more of the coffee's acidity.
The result can be that a coffee is perceived as less fresh or lively.
If the alkalinity is lower, more of the coffee's natural acidity will be able to be experienced in the cup.
This does not mean that high or low alkalinity is always best.
A very fruity and acidic coffee can, for example, be perceived differently with water with higher alkalinity than with water with lower alkalinity.
The water therefore becomes part of the overall flavor balance.
Is pH the most important number?
No.
pH tells you something about the current acidity or alkalinity of the water, but it does not alone tell you how the water reacts with the acids in coffee.
Two types of water can have almost the same pH and still affect a cup of coffee differently.
For coffee brewing, it is therefore often more interesting to know, among other things:
- alkalinity
- hardness
- total mineral content.
You usually do not need to measure all of this at home.
But it explains why two types of water, which both taste neutral on their own, can produce different coffee.
What role do calcium and magnesium play?
Calcium and magnesium are among the most important minerals when talking about water hardness.
They can affect how different compounds are extracted from the coffee.
Therefore, changes in the ratio between the minerals can also change the taste experience.
This does not, however, mean that you need to try to create a specific magnesium or calcium recipe at home.
For regular home brewing, it is more important to first find out if your existing water works well.
Taste the coffee with your normal water.
Compare if necessary with filtered water.
If the difference is clear, you know that water is a variable worth working on.
Can water be too soft?
Yes.
Very low mineral content is also not necessarily optimal for coffee brewing.
Pure distilled or fully demineralized water contains almost no minerals and therefore behaves differently during brewing than ordinary drinking water.
It can both affect the taste and be inappropriate for certain types of coffee equipment.
Therefore, do not automatically use distilled or fully demineralized water in an espresso machine.
Always follow the machine manufacturer's requirements for water quality.
If you work with demineralized or reverse osmosis water for specialty coffee, the water is usually remineralized afterwards.
Is spring water or bottled water better for coffee?
Not automatically.
Bottled water can have very different mineral contents.
Some types have relatively few minerals, while others are very mineral-rich.
Therefore, “bottled water” is not one specific type of water.
If you want to try bottled water for coffee, you should look at the mineral content rather than just the label on the bottle.
The same applies to spring water.
The fact that the water comes from a spring does not automatically mean that it has the optimal composition for coffee brewing.
Can I use regular tap water for coffee?
Yes.
If your tap water tastes good and gives a satisfactory result in the cup, there is no reason to make the water treatment more complicated than necessary.
Tap water does, however, vary from area to area.
Two people can therefore follow exactly the same coffee recipe with the same coffee beans and still get slightly different results because the water is different.
If you move or brew coffee somewhere else and suddenly find that the coffee tastes different, the water may be part of the explanation.
How do I find the hardness of my water?
Your local water utility or water supply company can usually provide the water's hardness and other analysis results.
You can also measure the water's hardness with various test strips or test kits.
If the purpose is primarily to set up an espresso machine or assess the need for filtration, a simple hardness test can be useful.
If you want to work more advanced with brewing water, you can also measure, for example, alkalinity and total hardness separately.
For most home brewers, however, it is not necessary to start with a complete water laboratory.
Start by finding the water utility's data and tasting the result.
What does °dH mean?
In Denmark, water hardness is often stated in German degrees of hardness, written as:
°dH
The higher the number, the harder the water.
You may therefore encounter terms such as:
- very soft
- soft
- medium hard
- hard
- very hard water.
When you read international guides on coffee, hardness may instead be stated in milligrams per liter or ppm calculated as calcium carbonate.
Therefore, the numbers cannot always be compared directly without conversion.
What is TDS?
TDS stands for Total Dissolved Solids and describes the total amount of dissolved substances in the water.
It is often measured in ppm.
A TDS number does not, however, tell you exactly which minerals the water contains.
Two types of water with the same TDS can therefore have different compositions and affect coffee differently.
TDS can be a useful indicator, but it does not tell the whole story about brewing water.
Is filtered water better for coffee?
It can be.
It depends on what the filter does to the water.
Some filters reduce, among other things, chlorine and certain unwanted flavor substances.
Other systems also reduce some of the water's hardness.
This can both change the coffee's taste and reduce limescale formation.
But a water filter does not automatically make all water perfect for coffee.
The result depends on both the water before filtration and the filter type itself.
If your tap water already works really well, the difference may be small.
If, on the other hand, the water is very hard or has a distinct taste or odor, the difference may be greater.
What does a water filter do in an espresso machine?
Some espresso machines have a filter directly in the water tank.
The filter's function depends on the model.
An example is the Sage ClaroSwiss, which filters the water in compatible Sage machines and helps to reduce, among other things, chlorine, heavy metals and limescale formation.
You can see our Sage ClaroSwiss water filter, if you have a compatible Sage machine.
A water filter does not, however, necessarily mean that the machine never needs to be descaled.
Always follow the manufacturer's maintenance program.
Water filter and descaling are not the same
It is important to distinguish between the two.
A water filter treats the water before or while it enters the machine.
Descaling removes mineral deposits that have already formed in the machine.
A water filter can therefore help to reduce limescale formation, but it does not necessarily replace descaling.
If your machine notifies you that it needs to be descaled, you should follow the manufacturer's procedure.
You can find descaling agents and water filters in our cleaning and care for coffee machines.
How does water affect coffee with high acidity?
The coffee's perceived acidity is influenced, among other things, by the water's alkalinity.
Higher alkalinity can neutralize more of the coffee's acids and thus dampen some of the perceived acidity.
Lower alkalinity can make the acidity more prominent.
This means that the same light-roasted, fruity coffee can be perceived differently with two different types of water.
If a coffee that should be fresh and lively consistently tastes flat, the water may be worth investigating.
Conversely, a distinct acidity is not automatically a problem.
Acidity can be a natural and desired part of the flavor profile in, for example, light-roasted coffees.
What if the coffee tastes flat?
Water can be one possible cause.
If the water has high alkalinity, part of the coffee's acidity can be neutralized.
But you shouldn't start by blaming the water for everything.
Flat coffee can also be caused by:
- old coffee beans
- grinding that is too coarse
- low extraction
- incorrect dosage
- insufficient brewing temperature.
Therefore, start with a stable recipe.
If the rest is working, you can then compare different types of water.
What if the coffee tastes very sharp or acidic?
It can also have several causes.
A very coarse grind size or insufficient extraction can result in a sharp and underdeveloped cup.
But water with low alkalinity can also make the coffee's natural acids more prominent.
That is why you should change one thing at a time.
If you adjust the grind size, temperature, dosage, and water all at once, it becomes almost impossible to know what made the difference.
Use our grind size guide if you want to check your grind first.
Water for filter coffee and pour over
For filter coffee, V60, and Chemex, the water is a very distinct ingredient because the drink has a relatively high ratio of water to coffee.
This makes the water’s composition interesting, especially when brewing lighter coffees with clear notes of fruit and acidity.
Use fresh water that tastes clean.
If your tap water is very hard or clearly affects the coffee, try filtered water and compare the result.
You can find the entire brewing process in our guide to filter coffee or among our complete brewing guides.
Water for espresso
For espresso, water has two roles.
It must contribute to a good extraction, but it must also function safely in a machine with a boiler, valves, heating elements, and narrow water paths.
This makes water quality particularly important.
Very limescale-forming water can cause problems over time.
Conversely, you should not use extremely mineral-poor or aggressive water in an espresso machine without knowing that the manufacturer accepts it.
Therefore, always follow the espresso machine's water requirements.
If the machine uses a water filter, it must be replaced according to the manufacturer's instructions.
If you have problems with the espresso extraction itself, you can also see our guide to espresso.
Water for French press and AeroPress
The same basic principles apply here as well.
The water must taste clean and have a mineral composition that works for the coffee.
However, a French press and AeroPress do not have the same technical limescale issues as an espresso machine with an internal boiler, if, for example, you heat the water separately in a standard kettle.
The water may still form limescale in the kettle, but the brewer itself is much easier to maintain.
Therefore, you can experiment with brewing water for manual brewing methods without having to take the exact same precautions as with an expensive espresso machine.
Should I buy specialty water for coffee?
For most people, it is not necessary.
Start with your regular water.
If the coffee tastes good, there is no reason to make the brewing process more complicated.
If you want to experiment, you can compare:
- your regular tap water
- filtered tap water
- another suitable drinking water with a known mineral content.
Use the same:
- coffee
- grind size
- dosage
- temperature
- brewing time.
Then taste the coffees side by side.
This is a much more practical way to get to know your water than just chasing a specific number.
Can you make your own water for coffee?
Yes.
Some coffee enthusiasts use demineralized or reverse osmosis water as a base and then add specific amounts of minerals.
This makes it possible to control both hardness and alkalinity very precisely.
It can be interesting for experiments, cupping, and advanced filter brewing.
But it requires precise dosage and an understanding of water chemistry.
For an expensive espresso machine, you should not use homemade water recipes without knowing whether the water meets the machine manufacturer's requirements.
Incorrectly composed water can both cause limescale problems and, in certain cases, be inappropriate for the machine's materials.
Should I use boiled water from the day before?
We recommend fresh water for coffee brewing.
Fill the amount of water you need when you are ready to brew.
Water that has been sitting for a long time in a coffee machine's reservoir or kettle is not necessarily the best starting point for a fresh cup of coffee.
For a standard filter coffee machine, you can therefore advantageously fill it with fresh, cold water before brewing.
Can limescale affect the taste of coffee?
The water’s mineral composition affects the taste, while actual limescale deposits are primarily a problem for the equipment.
If limescale builds up inside a coffee machine, it can affect the machine’s function and heat transfer.
Therefore, the machine should be descaled according to the manufacturer's recommendations.
If you want to learn more about the difference between descaling, backflushing, and regular cleaning, you can read our guide to cleaning an espresso machine.
How to find out if the water is limiting your coffee
You don't need to buy advanced measuring equipment first.
Perform a simple test instead.
1. Brew your normal coffee
Use your regular recipe and your normal tap water.
2. Brew it again with filtered water
Keep everything else as consistent as possible.
3. Taste side by side
Notice:
- acidity
- sweetness
- bitterness
- clarity
- body
- aftertaste.
4. Choose the cup you prefer
If the difference is small, you may not need to do anything more.
If the difference is significant, it may be relevant to investigate the water’s hardness and alkalinity more closely.
The most important thing is the result in the cup.
Good water doesn't have to be complicated
Water chemistry can become very technical.
But you don't need to know the concentration of every mineral to make good coffee at home.
Start with these principles:
- Use water that tastes good.
- Use fresh water.
- Avoid extreme levels of hardness or mineral deficiency.
- Take limescale seriously in coffee machines and espresso machines.
- Use filtration if your water or equipment benefits from it.
- Always follow the machine manufacturer's water requirements.
- Compare different types of water yourself if you want to improve the coffee further.
And remember:
Water is one variable among many.
Good coffee beans, appropriate dosage, the right grind size, and a stable brewing method are still crucial.
Frequently asked questions about water for coffee
Which water is best for coffee?
Water that tastes clean and has a moderate mineral content is a good starting point. The optimal water also depends on the coffee, the brewing method, and any requirements from the coffee machine.
Is hard water bad for coffee?
Not necessarily. Minerals are an important part of brewing water. Very hard water can, however, affect the taste and cause more limescale in coffee machines.
Is soft water best for coffee?
Not automatically. Very mineral-poor water can also give a worse brewing result and may be inappropriate in certain espresso machines.
Can I use tap water for coffee?
Yes. If the tap water tastes good and gives a satisfying result, it can certainly be used for coffee.
Is filtered water better for coffee?
It depends on your tap water and the filter. Filtration can be useful in cases of, for example, very hard water or unwanted taste, but it is not always necessary.
Can I use distilled water for coffee?
Pure distilled water contains almost no minerals and is usually not a good standard choice for coffee brewing. In particular, it should not be used in an espresso machine without checking the manufacturer's requirements.
What is alkalinity?
Alkalinity describes the water's ability to neutralize acid. In coffee, higher alkalinity can dampen some of the perceived acidity.
What does water hardness mean?
Water hardness is mainly related to the amount of calcium and magnesium. Hardness affects both coffee brewing and the risk of limescale deposits.
What is TDS in water?
TDS means Total Dissolved Solids and is a measure of the total amount of dissolved substances in the water. TDS, however, does not tell you exactly which minerals the water contains.
Does a water filter remove the need for descaling?
Not necessarily. A filter can reduce limescale formation, but the machine may still need descaling according to the manufacturer's instructions.
How do I find out how hard my water is?
Check the water analysis from your local water utility or use a suitable water hardness test.
Can water really change the taste of coffee?
Yes. Minerals and alkalinity affect both extraction and how, among other things, the coffee’s acidity is perceived.