Good Water for Coffee – The Ultimate Coffee Water Guide

Every coffee drink consists of at least 90% water. Filtered coffee even consists of over 98% water. Less than 2% are dissolved coffee particles (TDS). These figures show how important water is for brewing coffee. The coffee water should be neutral in taste and free from chlorine or other unwanted flavoring substances.

But even if water from your tap tastes good, it's not necessarily the best coffee water. The amount of minerals in your water has a decisive impact on the taste of your 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 the hardness of your water. We work out 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 decode any mineral water label and find suitable coffee mineral water to buy. 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 ZHAW in Wädenswil.

More articles about filtering coffee:

• Filtering with water filter pads
• Filtering with water filter cartridges
• Filtering with table water filters

What is good coffee water?

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

"Soft" refers to "hardness". For brewing coffee, we're mainly interested in two measurements: total hardness and alkalinity.

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

At this point, a water chemist would launch into a lecture. But for now, only the essentials matter.

Total hardness and alkalinity are measured in different units. We give you our recommendation for good coffee water in German degrees of hardness, but we'll explain further down 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: On water hardness test kits and other sources, carbonate hardness is mentioned instead of alkalinity. We go into this further down and use the more precise term alkalinity here in the text.

Do you need to know more to brew good coffee? Not necessarily. If you have this water available. Then enjoy your coffee. If not, then continue here.

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

The easiest thing is when the perfect water for brewing coffee comes straight from the tap. In some regions, that's the case. A few years ago, Benjamin traveled through Switzerland and tasted, measured, and brewed coffee with water from springs using the same protocol every time. In many regions of Valais, the water flows perfectly from the tap.

Water hardness can be measured with different equipment. A conductivity meter can provide information just as well as ppm meters. The simplest and cheapest way to measure is a drop test (titration tests). This allows you to easily measure total hardness and alkalinity.

10 ml is 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 hardness 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 table water filter does its job. It comes from well-known brands like BWT or Brita and other smaller brands. The table water filter decarbonizes only half of the water with each filtration. The other half only passes through an activated carbon filter. With 50% of the water, 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 work 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 from 12 °dH, 6 °dH alkalinity remains. We also reduce total hardness by 6 °dH, since this is removed as a pair. The result after the first filtration is 10 °dH GH and 6° dH alkalinity.

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

Admittedly, it's a tedious procedure. But one that works in many cases.

The water filter with fixed water connection



Water filters that are connected to fixed water supply have significantly higher filtration effectiveness through water pressure. Here, larger amounts of water can already be filtered in one water pass to the target range and beyond.

If the water becomes too soft, it can be adjusted to a desired target size by mixing 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 magnesium and calcium are replaced by hydrogen ions, which are bound to bicarbonate. This reduces total hardness and alkalinity equally. 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's 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 caused by water that is too hard.



Installation on your home water line should be done by professionals, especially in rental apartments. Ultimately, however, it's not complicated. The fixed water filter can be connected to the cold water line in the kitchen via a T-piece. If no additional hole can be drilled into the work surface in rental apartments, we recommend simply converting the cold water tap to a "filter water tap". To do this, no T-piece is inserted into the line; instead, all cold water is completely run through the filter and drawn from 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 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 bicarbonate.

On mineral water bottles, the total mineralization is usually given in mg/L. With this, we can calculate German hardness. Calcium is heavier than magnesium but lighter than bicarbonate.

Read the mg/L from your water bottle for calcium, magnesium, and bicarbonate and enter these into the formula. Further down for those interested, the derivation.

Example Volvic:

Mineral	Value	Calculation
Calcium	12 mg/L	÷ 7.1 = 1.69° d
Magnesium	8 mg/L	÷ 4.35 = 1.84° d
Total hardness	3.53° d GH
Bicarbonate	74 mg/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 so that lime is formed.

• For calcium, it's 40mg/L versus 100mg/L bicarbonate. Thus the factor is 2.5.
• For magnesium, it's 24mg/L, and accordingly the factor is 4.1.
• For bicarbonate, the factor is 0.82

When we use these, we get a value in parts per million calcium carbonate, which gives 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 an intermediate step.

• That means: calcium in mg/L divided by 7.1 plus magnesium in mg/L divided by 4.35 equals total hardness.
• The bicarbonate value in mg/L is divided by 21.8 to calculate alkalinity in dH.

Ignore all other values on the bottle for now.

Mixing mineral water and tap water

Mixing can also work. Harder water and very soft water together can create the perfect water. A higher tap water ratio reduces the water costs for buying mineral water.

The following calculation helps you mix two waters so that your target water is created. Have fun mixing.

Demineralization systems are a coffee water problem!

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

Alkalinity can also be described as acid buffering capacity. In nature, this is a good effect because acidic water is "reversed". For coffee, this is problematic. Coffee — like many complex delicacies — lives from acids that are balancing and stabilizing for coffee flavor. When these acids are buffered by high alkalinity, the result is flat and dull coffee. The finest coffees in the world then taste like standard coffee and lose their characteristics. Therefore, while demineralization systems are advantageous for reducing scale formation, they are problematic for preparing coffee water.

In houses with demineralization systems, the only option usually is the garden. As a rule, water hoses are not connected to the demineralization system. Here the process of measuring and filtering via decarbonization or switching to mineral water begins again.

Important

Demineralization systems are not suitable for preparing good coffee water!

Basics about water

Minerals are basically 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 refers to the equality between alkalinity and mostly calcium, since lime 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 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 values are also given in ppm (parts per million)
• pH value is also measured, which in most water is around the neutral value of 7. Rainwater, for example, is already acidic due to the contained carbon dioxide, with a pH value of approx. 5.5

Unit	ppm CaCO₃	°d	°f	Ca²⁺ + Mg²⁺ (mmol/L)	HCO₃⁻ (mmol/L)	Ca²⁺ (mg/L)	Mg²⁺ (mg/L)	HCO₃⁻ (mg/L)
1 ppm CaCO₃ =	1	0.05603	0.1	0.009991	0.01998	0.4004	0.2428	1.219
1 °dH =	17.85	1	1.785	0.1783	0.3566	7.147	4.334	21.76
1 °fH =	10.00	0.5603	1	0.09991	0.1998	4.004	2.428	12.19
1 mmol/L (Ca²⁺+Mg²⁺) =	100.1	5.608	10.01	1	–	40.08	24.30	–
1 mmol/L (HCO₃⁻) =	50.04	2.804	5.004	–	1	–	–	61.02
1 mg/L (Ca²⁺) =	2.497	0.1399	0.2497	0.02495	–	1	–	–
1 mg/L (Mg²⁺) =	4.118	0.2307	0.4118	0.04114	–	–	1	–
1 mg/L (HCO₃⁻) =	0.8202	0.04595	0.08202	–	0.01639	–	–	1

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

Basically, water consists of equal parts total hardness (magnesium and calcium) and alkalinity (bicarbonate). But 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 even after filtration.

Only a demineralization process would help, which should then 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 total hardness to about 14° dH with a sodium exchange.
2. Then reduce both to 4° dH GH and 2° dH alkalinity with a conventional decarbonizer.

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

Danger zones for scale 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 Expert Group e. V.