Water filter pads for espresso machines – use and problems

Water filter pads serve one purpose: they are meant to filter hard water. The risk of limescale buildup in espresso or coffee machines should be reduced and the water should be improved in taste. We tested four water filter pads and the conclusion is disappointing: all four fail to achieve either or both of these goals when used according to manufacturer instructions.

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

Good water for coffee preparation

In many places, tap water at home is too hard to prepare sensory-good coffee. Just as problematic is the fact that even moderately hard water causes limescale buildup. We explained what good water for coffee preparation is in a detailed article and video. Here are the key parameters 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 to measure these values at home, what they mean, and how to change them is also explained in the linked article. https://kaffeemacher.ch/kaffeewasser/

We were often asked whether this water quality could also be achieved with water filter pads or water filter cartridges.

Using water filter pads

Water filter pads are rinsed according to manufacturer instructions and then placed in the water tank of an espresso machine or fully automatic coffee maker. There, the water filter pads soften or decarbonize the water over time.

Different manufacturers provide different specifications.

For example, ECM recommends a soaking time of 15 hours for water hardness of 15. BWT recommends use overnight (8 – 10 hours according to the application brochure). None of the four manufacturers take into account the initial hardness of the water. It is only mentioned for the pad's lifespan (maximum 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. When do we typically refill water? When the espresso machine complains about low water level or the fully automatic coffee maker beeps annoyingly.

So we add water and then brew coffee. Nobody waits overnight until the next brew or even 3 – 4 days, which our measurements suggest would be necessary.

How effective are water filter pads?

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

Total hardness developed as follows.

Total hardness development of water filter pad

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

While the water filter pads from BWT and BRITA had sufficiently reduced alkalinity after 100 hours, this value remained constantly too high for the ECM and Rocket water filter pads. These two pads do soften the water, but do not replace the bicarbonate to the same degree.

While the water is thus protected against limescale formation, it remains sensory problematic. High alkalinity leads sensorily to a strong suppression of any acidity in the coffee. However, this acidity is necessary for coffee to be balanced and not taste flat.

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

Michel Aeschbacher

Water filter pads as false advertising

The slow filtering effect of the pads requires deliberate use if they are to make any sense at all. Used as described by manufacturers in the instructions, they are not effective and endanger your espresso machine while also ensuring that coffee doesn't taste good.

The water filters from Rocket and ECM are in our view not suitable for brewing good coffee from a sensory perspective. While they protect your machine if left in 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. They work best in a separate water jug with a water filter pad placed in the refrigerator and left in contact for an appropriate length of time depending on initial hardness. We have described here how you can determine your initial hardness.

Inline filters and water filter cartridges that are inserted directly into the water canister work better. Due to the flow-through effect, the filtering performance is significantly better. We have written a test article about this.

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Backup information

Alkalinity and total hardness were measured with titration drop tests from BWT. A total of 2 liters of water was used and kept at room temperature in the water tank with 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

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