Some coffee machine filters can remove heavy metals from water, such as lead or copper. These substances can enter tap water, for example, from older plumbing or natural sources. The filter cartridge uses a special mixture for this purpose, most often a so-called ion exchanger. It is a resin that binds undesirable metal ions and replaces them with other, harmless substances. The result is cleaner water, which can have a positive effect on the taste of the prepared coffee.