Good water for coffee – the ultimate coffee water guide

Every coffee drink consists of at least 90% water. A filter coffee even consists of over 98% water. Less than 2% are dissolved coffee particles (TDS). These figures illustrate how important water is for coffee preparation. The coffee water should be tasteless and free of chlorine or other foreign-tasting substances.

But even if the water from your tap tastes good, it is not necessarily the best coffee water. The amount of minerals in your water has a decisive influence on the taste of the coffee and 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 will show you which filtering method brings your water into the target range. Water from some regions is not well suited for brewing delicious coffee, even with filtering. A "mineral water calculator" helps you decipher any mineral water label to buy suitable coffee mineral water. Another formula calculates the mixing ratios between two waters 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.

Further articles on coffee filtering:

• Filtering with water filter pads
• Filtering with water filter cartridges
• Filtering with tabletop water filters
• All articles on coffee and water.

What is good coffee water?

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

"Soft" refers to "hardness". For coffee preparation, we are mainly interested in two quantities: 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. But for now, only the most important things matter.

Total hardness and alkalinity are given in different units of measurement. Here we give you our recommendation for good coffee water in German hardness, but further down we explain how you can convert 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: Test kits for measuring water hardness and other sources refer to carbonate hardness instead of alkalinity. We will discuss this further 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 available. Then enjoy your coffee. If not, then read on.

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

The easiest way is if the perfect water for brewing coffee comes from the tap. In some regions, this is the case. A few years ago, Benjamin traveled through Switzerland, tasting and measuring water from springs and brewing coffee according to the same protocol. In many regions of Valais, the water flows perfectly from the tap.

The hardness of water can be measured with different devices. A conductivity meter can provide information, as can ppm meters. The simplest and cheapest method of measurement is a drop test (titration tests). This allows for easy measurement of total hardness and alkalinity.

10 ml are placed in 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 degree is reached, the mixture in the test tube changes color. This indicates the effective hardness of the domestic water.

How and what does the tabletop water filter filter?

A tabletop water filter does its job. It is available from well-known brands like BWT or Brita and other smaller brands. The tabletop water filter decarbonizes only half of the water with each filtering. The other half only runs through an activated carbon filter. For 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'll 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. This is our starting point. From 50% of the water, we remove all alkalinity and exactly the same amount of total hardness, as we can only ever remove pairs of total hardness and alkalinity.

So, 12 °dH becomes 6 °dH alkalinity. Similarly, we reduce the total hardness by 6 °dH, as these are removed as a pair. The result after the first pass is 10 °dH GH and 6° dH alkalinity.

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

Admittedly, a complex process. But one that works in many cases.

The water filter with fixed water connection

Water filters connected to the mains water supply have a significantly higher filtering effectiveness due to the line pressure. Here, larger quantities of water can be filtered to and beyond the target range with just one pass.

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

In decarbonization, ion exchange occurs, in which magnesium and calcium are replaced by hydrogen ions, which are bound to hydrogen carbonate. This reduces both total hardness and alkalinity 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, then a permanently installed filter system is a very good solution. It is very convenient and guarantees the longevity of your high-quality equipment. Compared to the acquisition costs of an espresso machine and grinder, the costs for installing a filter system are manageable. Over 90% of all machine defects are due to excessively hard water.

The installation on the domestic water pipe, especially in rented apartments, should be carried out by specialists. Ultimately, however, it is not complicated. The fixed water filter can be connected to the cold water pipe in the kitchen via a T-piece. If an additional drill hole in the worktop is not permitted in rented apartments, we recommend simply converting the cold water tap into a "filter water tap". In this case, no T-piece is installed in the pipe, but the cold water is completely passed through the filter and drawn off via the tap.

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

Mineral water as coffee water

Who hasn't experienced this? You're on vacation and want to brew 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.

On mineral water bottles, the total mineralization in mg/L is usually given. 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. Further below, for those interested, the derivation.

Example Volvic:

• Calcium 12mg/L / 7.1 = 1.69° d
• Magnesium 8mg/L / 4.35 = 1.84° d
• Total 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 is formed.

• 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

If we use this, we get a value in Parts per Million Calcium Carbonate, which gives us the effective amount of particles. Since this then has to be divided by 17.85 to reach German hardness, we take the direct route without an intermediate step.

• That 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 now.

Mixing mineral water and tap water

Mixing can also work. A harder water and a very soft water combined can result in the perfect water. A higher proportion of tap water reduces the water costs for buying mineral water.

The following calculation will help you to mix two waters to achieve your target water. 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 by sodium. This greatly 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 - like many complex luxury foods - thrives on acids that balance and stabilize the coffee flavor. If these acids are buffered by high alkalinity, the coffee subsequently tastes bland and dull. The finest coffees in the world then taste like uniform coffee and lose their characteristics. Therefore, desalination plants are advantageous for reducing limescale formation, but problematic for preparing coffee water.

In houses with desalination plants, the only option is usually to go to 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 or reaching for mineral water begins again.

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

Basics about water

Minerals are fundamentally uncharged. Dissolved in water, they break down 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)

Carbonate hardness refers to the equality between alkalinity and mostly calcium, as limescale can be formed 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 includes all minerals in the water, as well as salts.
• Conductivity also measures all minerals in the water in Micro Siemens μ S/cm.
• Often all data is also given in ppm (Parts per Million)
• The pH value is also measured, which for most waters is around the neutral value of 7. Rainwater, for example, is already acidic due to the carbonic acid it contains, with a pH value of approx. 5.5.

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

Fundamentally, 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 by normal filters. Thus, the difference between GH and alkalinity remains the same despite filtering.

Only desalination would help here, which would then 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 a sodium exchange.
2. Then reduce both to 4° dH GH and 2° dH alkalinity with a classic decarbonizer.

Alternatively, reverse osmosis can be used to exchange the entire mineralization and re-enrich it with magnesium and calcium.

Hazard 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 Tegernsee Specialist Group e. V.