Good water for coffee – the ultimate coffee water guide

Every coffee drink consists of at least 90% water. Filter coffee is actually over 98% water. Less than 2% consists of dissolved coffee particles (TDS). These figures illustrate just how important water is for preparing coffee. The brewing water should be flavor-neutral and free from chlorine or other off-tastes.

But even if the water from your tap tastes good, it isn't necessarily the best coffee water. The amount of minerals in your water has a decisive impact on the taste of the coffee as well as the longevity of your coffee or espresso machine.

In our coffee water guide, we recommend the appropriate water hardness for filter coffee and espresso. You will learn how to determine the hardness of your water. We explain which filtration method will bring your water into the target range. Water from some regions is not well-suited for brewing delicious coffee, even after filtration. A "mineral water calculator" helps you decipher any mineral water label so you can buy the right mineral water for coffee. Another formula calculates the mixing ratios between two types of water to achieve a target water.

The foundations for this article were developed by Michel Aeschbacher. Many thanks for the support to Otto Wyss from BWT and Dr. Marco Wellinger from the ZHAW in Wädenswil.

More articles on filtering coffee:

• Filtering with water filter pads
• Filtering with water filter cartridges
• Filtering with pitcher water filters
• All articles on the topic of coffee and water.

What is good coffee water?

Good water for preparing coffee is very soft. Soft water has absorbed a low amount of dissolved and decomposed minerals.

"Soft" refers to "hardness." For coffee preparation, we are mainly interested in two values: total hardness and alkalinity.

• Total hardness = Magnesium Mg+2 and Calcium Ca2+
• Alkalinity = Hydrogen carbonate = Bicarbonate = HCO3-

At this point, a water chemist would launch into a lecture. For now, however, here is the most important part.

Total hardness and alkalinity are given in different units of measurement. We provide our recommendations for good coffee water in German degrees of hardness (°dH) here, but explain below how you can convert to all other units.

Perfect water for filter coffee:

• Total hardness: 2 – 3 °dH
• Alkalinity: 1 – 2 °dH

Perfect water for espresso:

• Total hardness: 3 – 6 °dH
• Alkalinity: 2 – 4 °dH

Alkalinity vs. carbonate hardness: On test kits for measuring water hardness and in other places, people speak of carbonate hardness instead of alkalinity. We will address this below and use the more precise term alkalinity here in the text.

Do you need to know more to brew good coffee? No, not necessarily. If you have this water at hand, then enjoy your coffee. If not, then read on here.

What kind of water do I have at home? Let's measure together

The easiest thing is if the perfect water for preparing coffee comes straight out of the tap. This is the case in some regions. A few years ago, Benjamin traveled across Switzerland, tasting and measuring water from springs and brewing coffee using a consistent protocol. In many regions of the Valais, the water comes out of the tap perfectly.

Water hardness can be measured with various devices. A conductivity meter can provide information, as can a ppm meter. The simplest and most cost-effective method for measurement is a drop test (titration test). This allows you to easily measure total hardness and alkalinity.

10 ml are poured into the clean plastic test tube. Then, the analysis drops are added one by one. Each drop represents one degree of hardness. When the water's hardness level is reached, the mixture in the test tube changes color. This indicates the effective hardness of your home water.

How and what does the pitcher water filter filter?

A pitcher water filter does its job. It is available from well-known brands like BWT or Brita, as well as other smaller brands. With every filtration cycle, the pitcher water filter decarbonizes only half of the water. The other half just runs through an activated carbon filter. In 50% of the water, the total hardness and alkalinity are not affected, while the other 50% of the water is decarbonized to a maximum.

Let's calculate an example. We will go through another example in our water video.

From our tap, we measured water with a hardness of 16° dH total hardness and 12° dH alkalinity. That is our starting point. From 50% of the water, we remove all the alkalinity and exactly the same amount of total hardness, since we can only remove pairs of total hardness and alkalinity.

So, 12° dH becomes 6° dH alkalinity. We also reduce the total hardness by 6° dH, as it is removed as a pair. The result after the first pass is 10° dH GH and 6° dH alkalinity.

Now, we can again halve only the alkalinity with the second filtration, but the 4° dH difference in total hardness remains. Thus, after the second filtration, we reach a value of 7° dH GH and 3° dH alkalinity. This puts us almost in the target range for the desired coffee water hardness. A further filtration brings us into the perfect target range for espresso with 5.5° dH GH and 1.5° dH alkalinity.

Admittedly a laborious procedure, but one that works in many cases.

Water filter with fixed water connection

Water filters connected to the fixed water supply have a significantly higher filtration efficiency due to the line pressure. Here, larger quantities of water can be filtered into the target range and beyond in just one pass.

If the water becomes too soft, it can be adjusted to a desired target value by blending it with tap water. The difference between total hardness and alkalinity also remains with the filter cartridge.

During decarbonization, an ion exchange takes place in which magnesium and calcium are replaced by hydrogen ions, which are bound to hydrogen carbonate. As a result, both total hardness and alkalinity are reduced in equal parts. The pH value increases the more we filter.

For whom is a fixed water connection the right solution?

If you drink a lot of coffee and have hard water, a permanently installed filter system is a very good solution. It is very convenient and guarantees the longevity of your high-quality equipment. In relation to the purchase costs of an espresso machine and grinder, the costs for installing a filter system are manageable. Over 90% of all machine defects can be traced back to water that is too hard.

The installation on the home water pipe should be carried out by professionals, especially in rental apartments. Ultimately, however, it is not complicated. The fixed water filter can be connected to the kitchen's cold water pipe via a T-piece. If, in rental apartments, no additional hole may be drilled into the countertop, we recommend simply converting the cold water faucet into a "filter water faucet." To do this, no T-piece is installed in the line; instead, the cold water is passed entirely through the filter and drawn through the faucet.

The hot water remains "normal" water and can be used without accelerating the consumption of the filter cartridge.

Mineral water as coffee water

Who doesn't know this? You're on vacation and want to brew yourself some delicious coffee. Your hand grinder and your favorite beans are ready. But the tap water tastes like chlorine or smells unpleasant, and the coffee doesn't taste good.

Mineral water from the supermarket can be the solution. But the information on the bottle is overwhelming. What do sulfate and chloride have to do with my total hardness? How do I find out the total hardness to find the right coffee water?

Our mineral water calculator can help you. In principle, you only need three values: calcium, magnesium, and hydrogen carbonate.

As a rule, the total mineralization in mg/L is indicated on mineral water bottles. With this, we can calculate the German hardness. Calcium is heavier than magnesium but lighter than hydrogen carbonate.

Read the mg/L from your water bottle for calcium, magnesium, and hydrogen carbonate and enter them into the formula. Below, for those interested, is the derivation.

Example Volvic:

• Calcium 12mg/L / 7.1 = 1.69° d
• Magnesium 8mg/L / 4.35 = 1.84° d
• Total hardness: 3.53° d GH
• Hydrogen carbonate 74mg/L / 21.8 = 3.39
• Total alkalinity: 3.39° d Alk

The calculation is based on the amount of calcium or magnesium we need in relation to hydrogen carbonate, so that limescale forms.

• For calcium, it is 40mg/L compared to 100mg/L hydrogen carbonate. Thus the factor is 2.5.
• For magnesium, it is 24mg/L, and accordingly, the factor is 4.1.
• For hydrogen carbonate, the factor is 0.82

When we apply this, we get a value in parts per million calcium carbonate, which tells us the effective amount of particles. Since this must then be divided by 17.85 to reach German hardness, we take the direct route without an intermediate step.

• This means: Calcium in mg/L divided by 7.1 plus magnesium in mg/L divided by 4.35 results in the total hardness.
• The value of hydrogen carbonate in mg/L is divided by 21.8 to calculate the alkalinity in dH.

Ignore all other values on the bottle for the moment.

Mixing mineral water and tap water

Mixing can also do the trick. A harder water and a very soft water combined can result in the perfect water together. A higher share of tap water reduces the water costs for purchasing mineral water.

The following calculation helps you to mix two waters in such a way that your target water is created. Have fun mixing.

Desalination plants are a coffee water problem!

Desalination plants supply entire houses with water. Here, too, ions are exchanged, namely calcium and magnesium for sodium. This significantly reduces the total hardness of the water. However, the alkalinity remains.

Alkalinity can also be described as acid-binding capacity. In nature, this is a good effect because it "reverses" acidic water. For coffee, this is problematic. Coffee lives—like many complex luxury foods—from acids that are balancing and stabilizing for the coffee taste. If these acids are buffered by a high alkalinity, the coffee ends up bland and dull. The finest coffees in the world then taste like ordinary coffee and lose their characteristics. Therefore, while desalination plants are an advantage for reducing limescale formation, they are problematic for preparing coffee water.

In houses with desalination plants, there is usually only the option of going into the garden. As a rule, the water hoses are not connected to the desalination plant. This is where the process of measuring and filtering via decarbonization begins again, or opting for mineral water.

Important: Desalination plants are not suitable for preparing good coffee water!

Fundamentals of water

Minerals are generally uncharged. Dissolved in water, they decompose into charged fragments called ions.

• Cations = Positive equal to or greater than total hardness (sodium, potassium)
• Anions = Negative equal to or greater than alkalinity (sulfate chloride)

We refer to the equality between alkalinity and mostly calcium as carbonate hardness, since limescale can form from these. Example: 20° dH total hardness and 12° dH alkalinity equals 12° carbonate hardness

We measure using different methods:

• Total mineralization in mg/L is all minerals in the water, including salts.
• Conductivity is also all minerals in the water measured in micro Siemens μ S/cm.
• Often all information is also given in ppm (parts per million).
• The pH value is also measured, which for most water is around the neutral value of 7. Rainwater, for example, is already acidic due to the carbon dioxide it contains, with a pH of approx. 5.5

Where does the difference between total hardness and alkalinity come from?

Basically, water consists of equal parts total hardness (magnesium and calcium) and alkalinity (hydrogen carbonate). However, this is very often not the case because another mineral is added, namely gypsum. Gypsum consists of calcium (positive) and sulfate (negative). This is usually the difference between GH and alkalinity and cannot be reduced with normal filters. Thus, the difference between GH and alkalinity remains the same despite filtering.

Only desalination would help, but it would have to be adjustable so that not the entire amount of magnesium and calcium is exchanged.

Practical example: Raw water with 20° dH GH and only 12° dH alkalinity.

1. First, reduce the total hardness to about 14° dH with your sodium exchange.
2. Then, use a classic decarbonizer to reduce both to 4° dH GH and 2° dH alkalinity.

Alternatively, the entire mineralization can be exchanged via reverse osmosis and enriched again with magnesium and calcium.

Danger zones for limescale formation and corrosion

 

Source: https://www.bmlrt.gv.at/wasser/wasserqualitaet/grundwasser/karte_haerte_GW2017.html

Source: Water hardness map Germany: Mensch, Wasser, Sonne, Wärme & Umwelt, Issue 1997, environmental brochure of the Tegernseer-Fach-Gruppe e. V.