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Espresso coffee machines are affected by the quality of the water used in them. There are two main enemies, hardness salts and chlorine.

The normal accepted procedure for dealing with these problems is by a filtration method which employs the use of two different media, resin and carbon.


The resin attracts the temporary hardness salts – calcium carbonate and magnesium carbonate – which we normally identify as scale, as well as heavy metals. Although this is a water softening process it should not be confused with general water softeners (which are sodium based and inappropriate for use with potable water applications) and they are classed as dealkalisers (dealk). Whereas water softeners can be regenerated at point of use using salt, a dealk unit cannot be regenerated at point of use and has to be exchanged.

Like conventional water softeners the dealk resin is housed in a tank with inlet and outlet water connections. Most dealk units are available in different sizes and frequency of change depends upon water hardness  and volume of water used. The hardness level measured is the temporary hardness and not total hardness.


Carbon is used to remove organic matter and chlorine and this can either be incorporated within the resin tank or mounted as a separate unit.

Where the incoming water has low hardness salts and total dissolved solids the water supply may still contain undesired contaminants like chlorine and other tastes and odours. Where this is the case a simple sediment  prefilter to remove large particles should be installed and some form of carbon filter to remove the tastes and odours.


Reverse Osmosis is another form of filtration that is used in the specialist coffee industry. This form of treatment offers the end user or Barista the flexibility to adjust the product water to the desired total dissolved solids (TDS).

The Specialty Coffee Association (SCAA) created water standards that they deem necessary for a good brew. The odour and color are the two things that you can ensure without any testing. The water should be odour-free and the color should be clear. The chlorine content must be 0 mg/L. As mentioned earlier, total dissolved solids (TDS ) are important. The target goal should be roughly 150 mg/L (150ppm). The acceptable range for TDS is somewhere between 75–250 mg/L (75-250ppm). The calcium hardness should be about 4 grains or 68mg/L (70ppm).