Good water for coffee – the ultimate coffee water guide

Every coffee beverage consists of at least 90% water. A filter coffee is even more than 98% water. Less than 2% is total dissolved solids (TDS) . These figures illustrate how important water is for coffee preparation. Coffee water should be tasteless and free of chlorine or other impurities.

But even if water from your tap tastes good, it's not necessarily the best water for coffee. The amount of minerals in your water has a decisive impact 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'll learn how to determine your water's hardness. We'll explain which filtering method will bring your water into the target range. Water from some regions, even filtered, isn't suitable for brewing delicious coffee. A "mineral water calculator" helps you decipher every mineral water etiquette and thus buy the right mineral water for your coffee. Another formula calculates the mixing ratios between two types of water to achieve the desired water hardness.

Michel Aeschbacher provided the basis for this article. Many thanks to Otto Wyss of BWT and Dr. Marco Wellinger of the ZHAW in Wädenswil for their support.

More articles about filtering coffee:

• Filtering with water filter pads
• Filtering with water filter cartridges
• Filtering with table water filters
• All articles about coffee and water .

What is good coffee water?

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

"Soft" refers to "hardness." When preparing coffee, we are primarily interested in two parameters: total hardness and alkalinity.

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

At this point, the water chemist would launch into a lecture. But for now, only the most important points are covered.

Total hardness and alkalinity are measured in different units. Here we provide our recommendation for good coffee water in German hardness, but below we explain how to 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'll discuss this further below and use the more precise term alkalinity here.

Do you need to know more to brew good coffee? No, not necessarily. If you have this water handy, then enjoy your coffee. If not, continue here.

What kind of water do I have at home? We'll measure together.

It's easiest when the perfect water for making coffee comes from the tap. This is the case in some regions. A few years ago, Benjamin traveled through Switzerland , tasting and measuring spring water, and brewing coffee with it, always following the same protocol. In many regions of Valais, the water flows perfectly from the tap.

Water hardness can be measured using various devices. A conductivity meter can provide information, as can a ppm meter . The simplest and cheapest method is a drop test (titration test) . This allows you to easily measure total hardness and alkalinity.

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

How and what does the table water filter filter?

A countertop water filter does the job. They're available from well-known brands like BWT and Brita, as well as other smaller brands. A countertop water filter only decarbonizes half of the water each time it's filtered. The other half passes through an activated carbon filter. For 50% of the water, the overall hardness and alkalinity aren't affected, while the other 50% is decarbonized to the maximum.

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

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

So, 12 °dH becomes 6 °dH alkalinity. We also reduce the total hardness by 6 °dH, since this is taken as a pair. The result after the first run is 10 °dH GH and 6 °dH alkalinity.

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

Admittedly, it's a complex process, but one that works in many cases.

The water filter with permanent water connection

Water filters connected to the mains water supply have significantly higher filtration efficiency due to the mains pressure . Larger volumes of water can be filtered to the target area and beyond with a single pass.

If the water becomes too soft, it can be adjusted to the desired level by blending it with tap water. Even with the filter cartridge, the difference between total hardness and alkalinity remains.

During decarbonization , an ion exchange takes place, in which the magnesium and calcium are replaced by hydrogen ions bound to bicarbonate. This reduces the total hardness and alkalinity equally. The pH value therefore increases the more intensively we filter.

For whom is a permanent water connection the right solution?

If you drink a lot of coffee and have hard water, a permanently installed filter system is a great solution. It's very convenient and guarantees the longevity of your high-quality equipment. Compared to the initial cost of an espresso machine and grinder, the cost of installing a filter system is manageable. Over 90% of all machine defects are due to hard water.

Installation on the domestic water supply should be carried out by a professional, especially in rented apartments. Ultimately, however, it's not complicated. The fixed water filter can be connected to the kitchen's cold water line via a T-piece. If drilling an additional hole in the countertop isn't permitted in rented apartments, we recommend simply converting the cold water tap into a "filter water tap." To do this, no T-piece is inserted into the pipe; instead, the cold water is directed completely 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 a delicious cup of coffee. Your hand grinder and your favorite beans are ready. But the tap water tastes like chlorine or has an unpleasant smell, and the coffee tastes bad.

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

Our mineral water calculator can help you. Essentially, you only need three values: calcium, magnesium, and bicarbonate.

Mineral water bottles usually indicate the total mineralization in mg/L. This allows us to calculate the German hardness. Calcium is heavier than magnesium but lighter than bicarbonate.

Read the mg/L for calcium, magnesium, and bicarbonate from your water bottle and enter it into the formula. The derivation is below for anyone interested.

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 bicarbonate, which creates lime.

• For calcium, it's 40 mg/L compared to 100 mg/L for bicarbonate. 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 tells us the effective amount of particles. Since this must then be divided by 17.85 to achieve German hardness, we take the direct route without any intermediate steps.

• That means: Calcium in mg/L divided by 7.1 puls Magnesium in mg/L divided by 4.35 gives the total hardness.
• The value of bicarbonate in mg/L is divided by 21.8 to calculate the alkalinity in dH.

Ignore all other values ​​on the bottle for now.

Mix mineral water and tap water

The mix can also make a difference. Harder water and very soft water combined can create the perfect water. A higher proportion of tap water reduces the cost of purchasing mineral water.

The following calculation will help you mix two waters to create your desired water. Have fun mixing.

Desalination plants are a coffee water problem!

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

Alkalinity can also be described as the ability to bind acids . In nature, this is a good effect because it "turns around" acidic water. For coffee, this is problematic. Coffee—like many complex beverages—relies on acids, which balance and stabilize the coffee flavor. If these acids are buffered by high alkalinity, the coffee becomes bland and dull. The world's finest coffees then taste like generic coffee and lose their characteristics. Therefore, while desalination plants are beneficial for reducing limescale formation, they are problematic for treating coffee water.

In homes with desalination systems, the only option is usually to go to the garden. The water hoses are usually not connected to the desalination system. This is where the process of measuring and filtering water via decarbonization begins again, or the user resorts to mineral water.

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

Basics about water

Minerals are essentially uncharged. When 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 is defined as the balance between alkalinity and calcium, as calcium can form limescale. For 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 includes 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 waters is around the neutral value of 7. Rainwater, for example, is already acidic due to the carbon dioxide it contains, with a pH value of approximately 5.5.

Where does the difference between total hardness and alkalinity come from

Essentially, water consists of equal parts of total hardness (magnesium and calcium) and alkalinity (hydrogen carbonate). However, this is often not the case because another mineral, gypsum, is present. 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 this 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. Only with your sodium exchange will the total hardness be reduced to about 14° dH.
2. then reduce both to 4° dH GH and 2° dH alkalinity using a classic decarbonator.

Alternatively, the entire mineralization can be exchanged using reverse osmosis and re-enriched 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: People, Water, Sun, Heat & Environment, Issue 1997, environmental brochure of the Tegernseer-Fach-Gruppe e. V.