Coffee and water – How to use high quality water to brew the best coffee

A cup of coffee is actually 98 percent water. Make sure you use high quality water to make your coffee taste better!


A well balanced cup of coffee – something that we want to achieve when brewing. In case the taste turns out to be flat, hollow, bitter or vinegary, it is easy to assume that there is something wrong with the coffee beans or the brewing process.
As it turns out, there is 98 percent of water in our cup of coffee. It means that the quality of water has a significant role in the taste of coffee.  

There is water in my coffee! 
The transparent liquid H2O we are using as a base of all the coffee served hides a lot inside. Despite its transparency, there is a huge amount of solubles and solids in our tap water. This everyday consumable has a major effect on the quality of your cup of coffee. Also keep in mind: if the water is said to be of drinking quality, it might not be harmful for your health but can still contain some unpleasant substances that make your coffee taste flat or even bad.
Coffee brewing water should be clean and fresh by taste, smell and look. Also, it should be of food grade, and what’s more, there should not be chlorine, chloramine and hypochlorite in the water. This is a tough one due to the regular disinfecting of the main water pipes worldwide.
It is good to remember that fresh, cold water is always the best starting point for brewing coffee. You don’t want to ruin a good cup of coffee by taking hot water out of the tap. Tap hot water is not fresh and often has odd tastes and odors.


What exactly is water? 
What is there in water that effects the taste or quality of our coffee?
substances from soil, for example minerals and other organic substances
substances from water treatment, for example chlorine, which is added to the main water pipes to maintain microbiological quality standards
substances from the water supply system, for example copper and iron
residues from pollution
microbes – harmless ones, but also germs

Natural mineral water 
When the water meets carbonate rock containing magnesium carbonate and/or calcium carbonate, part of the water gains magnesium, calcium and bicarbonate ions.
You have probably heard the phrase “water hardness”. Sounds simple, right? Either there are lots of minerals in the water, or there are not? Well, here is a bit more detailed information.
Hardness in general describes the amount of dissolved minerals in water. Groundwater is harder than surface water because it has been in contact with minerals longer.

Total hardness (often measured as °dH): carbonate hardness + permanent hardness. In practice, this is the amount of Magnesium and Calcium ions.
Magnesium and Calcium are helping to extract more taste, so we for sure want some of them in our water. Not just too much – and  only with a reasonable amount of bicarbonate.
Magnesium makes a bit more powerful extraction than Calcium because a lot of flavorsome compounds are small and have a lot of oxygen in them. Magnesium likes these qualities.
Calcium easily bonds with other substances. Together with carbonate hardness level, for example, it causes formation of limescale.
Magnesium is not easily bonding, so it rarely causes limescale formation.

Carbonate hardness kH: Bicarbonate and some other carbonates originated from carbonic acid that are pairing up with Magnesium and Calcium.
Carbonate hardness is often quoted as temporary hardness. This actually makes sense, as boiling precipitates the minerals. When boiling water, the hardness is shifted from the water to the surfaces of the boiling equipment – for example a kettle or a coffee machine boiler. As a result, coffee machine valves can be clogged and achieving the right water temperature can be difficult.
Carbonates, however, are the kings of coffee brewing water. If we forget about them, they will turn our great cup of coffee into a misery. Carbonates are in charge of acid buffer capacity. This means ability to keep pH stabile – which does not necessarily mean neutral. Coffee contains weak acids by its nature. The acidity of the coffee batch is changing depending on the carbonate hardness due to the buffering capacity of the carbonates.

In case there is high carbonate hardness in water, the positive acidity in taste (i.e. citric, fruity, sour etc.) will be flushed away by the pH buffer. The acidity itself is still there, we just don’t find it in the taste, only the earthiness and dull, flat taste.
In case of low carbonate hardness the coffee taste is vinegary and sour. So a small amount of buffer should be kept.

Sometimes carbonate hardness is referred to as alkalinity, which is the capacity of an aqueous solution to neutralize acid. Keep in mind that alkaline or base means something else!
Permanent hardness: non-carbonate anions (= nitrates and sulfates) that are pairing up with Magnesium and Calcium. For example Sulfate and Calcium will form Gypsum.
Permanent hardness causes soft chalky or muddy sediment.

Other dissolved ions: In addition to Magnesium, Calcium and carbonates that form the hardness of water, there are other dissolved ions contributing to the taste of water. These are for example Sodium, Potassium, Nitrate and Chloride. These other dissolved ions cause a risk of corrosion in high ranges.

 What is here to be taken in? 
Overall content defines the character of water and furthermore the coffee brewed.
You could say low overall mineral content is usually worse than high overall mineral content. Also, low carbonate hardness must be compensated by lowering the total hardness because we want to have a positive balance between the minerals. Furthermore, high total hardness will increase the weak acids in the cup, and high carbonate hardness leads to huge crust when cupping but also means more frequent descaling for the coffee equipment.
At the end of the day, it is all about the balance between all the minerals in water.

Standards for high quality water 
Most waters worldwide are too high both in carbonate hardness and in total hardness. Treatment needed, that is!
SCA (Speciality Coffee Association) standards for minerals:
total hardness of 50-175 ppm CaCO3 (2,9-9,8 dH°)
carbonate hardness of 40-75 ppm CaCO3 (2,9-9,8 dH°)
total hardness should exceed carbonate hardness
pH of 6,5-8
(ppm equals here mg/l)
All this is to be studied based on the composition of the water in hand. Also, low brew ratios (fore example espresso compared to filter coffee) shift the optimum of  total hardness and carbonate hardness towards higher values. There are no exact numbers and ratios to be given!
What about pH of the water?
Basically water is neutral meaning it is of pH 7.  
However due to different molecules dissolved in water, it can also be slightly acidic or alcalic. As a result, regular drinking water in Europe can have pH ranging from ≥ 6,5 and ≤ 9,5.
The signification of pH for coffee, extremely simplified:
Acidic water is bad for extraction but good for flavor. Also, corrosion will be a problem for the equipment.
Basic water is good for extraction but bad for flavor.

Adjusting water for coffee?
If you are pondering is your water good for brewing coffee, you can start by checking the overall content of the water. When using water from the public water supply it is easy to check from the local water plant what does the water in the main water pipe actually contain. When using water from your own well you need to get an analysis on the water at your own expense. There are also different types of test sets available in the market for both household and professional use.

Based on the analysis or test result you are able to choose the correct method of adjusting the water setup.
At a café or a restaurant it might be a good idea to install a water filtration system if there is for example high carbonate hardness level in the water.
It is also possible to filtrate your water at home by using some of the equipment from the wide range of household filter sets.

Sometimes a UV light can be found in beverage equipment. It is to remove the impurities from for example drinking water dispensers. UV light destroys micro-organisms by interfering the biological process and perforating the cell walls. Combined to activated carbon, UV light block creates a good system to remove algae and other organisms. However it is not for manipulating the mineral content and definitely not to make drinkable water from contaminated water.

Is it worth all the trouble? 
It definitely pays off to check the brewing water quality.
Also, it pays off to even manipulate your water a bit to achieve more balanced cup of coffee.

Ask for the water content information from your local household water supplier and use the test sets available to see what there is in your water in in what quantities. 

Some of the most common and important substances regarding coffee brewing water  
Magnesium Mg2+
Calcium Ca2+
Magnesium carbonate MgCO3
Calcium carbonate CaCO3
Bicarbonate HCO3-
Carbonate CO32-
Carbonic acid H2CO3
Sulfate SO42-
Gypsum CaSO4·2H2O
Sodium Na+
Potassium K+
Nitrate NO3-

Chloride Cl−

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