Water filter pads for espresso machines – usage and problems

Water filter pads have one purpose: to filter hard water. The goal is to reduce the risk of limescale build-up in the espresso or coffee machine and to improve the taste of the water. We tested four water filter pads, and the conclusion is sobering: all four fail to achieve both goals, or do so only inadequately, when used according to the manufacturer's instructions.

We tested the water filter pads from ECM, Rocket O.SCA.R 90, BRITA Aqua Gusto 250, and BWT Bestsave S.

Good water for coffee preparation

In many places, local tap water is too hard to prepare coffee with a good flavor profile. At least as problematic is the fact that even moderately hard water promotes limescale build-up. We have explained what constitutes good water for coffee preparation in a detailed article and video. Here are the basic figures once again:

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

How you can measure these values at home, what they mean, and how to change them is also explained in the linked article.

We are often asked if this water can also be achieved using water filter pads or water filter pillows.

The use of water filter pads

Water filter pads are rinsed according to manufacturer instructions and then placed into the water tank of the espresso machine or fully automatic coffee machine. There, the water filter pads gradually soften or decarbonize the water.

Different instructions are given depending on the manufacturer.

ECM, for example, recommends a soaking time of 15 hours for a water hardness of 15. BWT recommends using it overnight (8 – 10 hours according to the application brochure). The initial hardness of the water is not taken into account by any of the four manufacturers. It is only mentioned regarding the shelf life of the pad (the maximum number of liters that can be filtered over time).

In any case, the pads need time to develop their filtering effect. This is where we stumble for the first time. Because when do we usually refill water? When the espresso machine flags a low water level or the fully automatic coffee machine starts beeping annoyingly.

So we top up the water and then brew our coffee immediately. No one waits overnight until the next cup, let alone 3–4 days, which our measurements suggest.

How effective are water filter pads?

We placed one filter pad from each manufacturer into a water tank filled with 2 liters of water. After 3 hours, 5 hours, 20 hours, and 100 hours, we measured the total hardness, alkalinity, and conductivity.

The total hardness developed as follows.

Total hardness development water filter pad

For all four pads, we were still not in the target range desirable for espresso after 20 hours, or, given an initial hardness of 16 GH °dH, we were still far from it. After 100 hours, all water filter pads had reduced the total hardness sufficiently, but not the alkalinity.

While the water filter pads from BWT and BRITA also sufficiently reduced the alkalinity after 100 hours, this value remained consistently too high with the water filter pad from ECM and Rocket. While both of these pillows soften the water, they do not replace the hydrogen carbonate to the same extent.

While the water is thus protected against limescale build-up, it remains sensorially problematic. High alkalinity leads to a strong attenuation of any acidity in the coffee. However, this is necessary for a coffee to be balanced and not taste bland.

Neither manufacturer communicates this on their packaging.

NOTE: As long as the water filter pad is in contact with the water, the water is in process and continues to be decarbonized or softened. An accurate determination of water hardness is only possible if you leave fresh water in contact with the pad for a specific amount of time. As soon as you add water, as usually happens in the water tank, the values become inaccurate again.

Michel Aeschbacher

Water filter pads as a deceptive package

The slow filtering effect of the pads requires targeted use if they are to make any sense at all. As described by the manufacturers in their instructions, they are not effective, put your espresso machine at risk, and also ensure that the coffee does not taste good.

In our view, the water filters from Rocket and ECM are not sensorially suitable for brewing good coffee. While they do protect your machine if they lie in the water for a long time, they do not reduce alkalinity.

The water filter pads from BRITA and BWT are theoretically usable, but must be used differently than described by the manufacturers. A separate water pitcher works best; place it in the refrigerator with a water filter pad and leave it in contact for the appropriate amount of time, depending on the initial hardness. We have described here how you can determine your initial hardness.

Plug-in filters and water filter cartridges that are inserted directly into the water container perform better. The flow suction makes the filtering performance significantly better. We have written a test article on this.

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Backup info

Alkalinity and total hardness were measured using titration drop tests from BWT. 2 liters of water were used in each case, kept at room temperature in the water tank with a water filter pad. Conductivity was also measured. The initial total hardness of our water is: 16 °dH total hardness, 13 °dH alkalinity, 520 conductivity.

Development of total hardness, water sample taken from the bottom.

Development of alkalinity, water sample taken from the bottom.

Conductivity development.

Conductivity	0 hrs.	3 hrs.	5 hrs.	20 hrs.	100 hrs.
Rocket	520	540	540	504	520
BWT	520	510	490	420	240
Brita 250	520	520	490	400	220
ECM	520	540	550	570	570