Water quality : the neglected ingredient
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Specialty Batch

Water quality : the neglected ingredient

A good cup of coffee is 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.


Let us understand the many aspects of the roasted and ground coffee Machine / product that are under the control of the coffee roasters and baristas that will also affect the rate of extraction and the flavour of the coffee beverage.  

The coffee variables are:

Bean originNot all beans have similar chemical composition.
Bean roastThe chemical composition of the coffee bean changes throughout the roasting process.
Size of coffee grindingsA consistent particle size is important, as the higher the surface area, the faster the extraction.
Dry mass of coffee grindingsA different extraction composition.
Temperature of extractionThe temperature dictates both the rate and composition of the extraction.
Pressure of extractionHas a similar effect as temperature.
Time of extractionIncreasing extraction time allows for greater extraction.
The waterThe variable is less obvious, but it is clear that the chemical composition of water (i.e. dissolved ions) plays a very important role.

As 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. What is there in water that effects the taste or quality of our coffee?

Water is so much more than just two parts of hydrogen to one-part oxygen. This seemingly simple compound provides a playground for all kinds of complex chemical interactions like…

  • 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

Coffee beverages are made up of about 98%-99% water. The remaining 1%-2% are brew solids that are extracted from the ground coffee.  At these rates, it is especially important to use high quality water along with fresh, high quality speciality coffee to produce coffee beverages.

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: 

CharacteristicTargetAcceptable Range
OdorClean / Fresh, Odor free
ColorClean color
Total Chlorine0 mg/L
Total Dissolved Solids150 mg/L75 – 250 mg / L
Calcium Hardness4 grains or 68 mg / L1-5 grains or 17mg/L – 85 mg/L
Total Alkalinity40 mg/LAt or near 40 mg/L
pH76.5 -7.5
Sodium10 mg/LAt or near 10 mg/L

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.

All this is to be studied based on the composition of the water in hand. Also, low brew ratios (for 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!

Hard Water Solutions

Places with hard water, above 150-200 ppm general hardness, will likely benefit from some form of mineral reduction. A few accessible options exist here; the two most common are ion exchange and reverse osmosis.

Cartridge systems can provide varying degrees of ion exchange, a system that passively ‘trades’ hard mineral ions for charged sodium or potassium salts. This typically increases the buffering alkalinity of a water, as well, and may lead to increased saltiness. However, many modern systems are highly programmable and precise. They have the added benefit of taking up relatively little space and producing little to no waste aside from regularly scheduled cartridge replacements.

Reverse osmosis uses a membrane to reduce the total dissolved content of water to very nearly zero. The resulting “empty” water is fed into a holding tank, while the minerals and other compounds blocked by the membrane must be flushed away. Most RO units will then reintegrate a portion of carbon-filtered water back into the demineralized water to achieve a target TDS. An independent pump and custom water lines are usually required to provide adequate line pressure and appropriate pathways to deliver the water to its intended destination.

If your water is especially hard, RO can provide an effective way to reduce its mineral content. However, there are some flaws. The amount of water required to flush the membrane, which goes down the drain (or, at best, can be reused as gray water), is significant. Factory settings for most RO systems can be in the range of 4 flushed gallons for every 1 gallon that’s kept. This is unfortunate, given that many places with especially hard water are also places prone to drought or otherwise restricted access to fresh, clean water. Draining away significant amounts of clean, treated (albeit hard) water may be a problem of its own.

The other potential complication with RO is that by blending a percentage of the source water back into the solution, you’re not really solving mineral imbalance problems. The water you’ve created is just a diluted version of what already exists. So, if your water is proportionally high in alkalinity, for example, RO water will not change that.

Soft Water Solutions

In soft water scenarios, at or below 50 ppm general hardness, some form of remineralization may be in order, both to help specialty coffee extract in ways that are delicious, but also to prevent the possibility of equipment corrosion due to low alkalinity.

This is a little more challenging than reducing minerals in hard water. There are cartridge options that exist; these are frequently some type of calcium or magnesium (crushed coral is a common option) that water flows over to add healthy hard minerals. In most cases, these cartridges depend on contact time. Thus, if the water is streaming at a constant rate through the system, relatively little of the mineral will dissolve. Conversely, if the water sits for a long time in the cartridge, it can result in a sudden spike in mineral content.

Systems exist that mineralize water; notably Global Customized Water offers options to inject their proprietary liquid formula in precise increments to optimize water for coffee (typically in the form of RO followed by liquid mineral addition). Third Wave Water has a similar, manual option that can mineralize distilled or deionized water in small batches by using pre-formulated dry mineral packets.

Ad hoc mineral addition is also possible. I’ve been experimenting with this a bit, and it requires a lot of attention to detail, an extremely precise scale, some moderate safety precautions, and some pretty good math. It does allow for highly customized water formulas, however. I keep sodium bicarbonate (baking soda) and potassium bicarbonate on hand for my alkalinity buffers. For minerals, the options include calcium and magnesium chlorides and sulphates. The sulphate forms I’ve found to be less readily soluble in water, often leaving a chalky, undissolved residue, so I tend to use the chlorides. Each of these minerals are easily available and inexpensive.


Specialty Batch Coffee is a Dubai-based, homegrown brand backed by a wealth of industry knowledge. With roots in Melbourne, Australia, we bring a solid 30+ years of combined specialty coffee experience & expertise to the table.

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