Water filter pads for espresso machines – use and problems

Water filter pads have one purpose: to filter hard water. They are intended to reduce the risk of limescale buildup in espresso or coffee machines and to improve the taste of the water. We tested four water filter pads, and the conclusion is sobering: none of the four achieve both goals, or only insufficiently, 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 preparing coffee

In many places, tap water at home is too hard to prepare sensorially good coffee. At least as problematic is that even medium-hard water promotes limescale formation. We have explained what good water for coffee preparation is in a detailed article and video. Here are the key data 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.

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

The use of water filter pads

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

Different manufacturers provide different instructions.

For example, ECM 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 water hardness is not considered by any of the four manufacturers. It is only mentioned for the pad's durability (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. Because when do we usually refill water? When the espresso machine signals a low water level or the automatic coffee maker beeps annoyingly.

So, we add water and then brew coffee. Nobody waits a night until the next brewing or even 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, which we filled with 2 liters of water. After 3 hours, 5 hours, 20 hours, and 100 hours, we measured total hardness, alkalinity, and conductivity.

The total hardness developed as follows.

Total hardness development of water filter pad

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

While the water filter pads from BWT and BRITA sufficiently reduced alkalinity after 100 hours, this value remained consistently too high for the water filter pad from ECM and Rocket. These two pads do soften the water, but they do not replace hydrogen carbonate to the same extent.

Thus, the water is protected against limescale formation, but remains sensorially problematic. High alkalinity leads sensorially to a strong weakening of any acidity in the coffee. However, acidity 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 the process and will continue 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 period. As soon as you add more water, as typically happens in the water tank, the values become inaccurate again.

Michel Aeschbacher

Water filter pads as a sham

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

In our opinion, the water filters from Rocket and ECM are not sensorially suitable for brewing good coffee. While they protect your machine if they remain 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. The best way is to use a separate water jug that you place in the refrigerator with a water filter pad, and leave it in contact for an appropriate amount of time depending on the initial hardness. We have described how you can determine your initial hardness here.

Better results are achieved with plug-in filters and water filter cartridges that are inserted directly into the water canister. Due to the flow suction, 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 using BWT titration drop tests. 2 liters of water were used in each case and 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 Std.	3 Std.	5 Std.	20 Std.	100 Std.
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