System for conditioning a liquid such as water, including: a first holder (5;25;35) of a medium for treating liquid, the medium in the first holder (5;25;35) including an ion exchange material loaded with at least a first counter ion species; and a second holder (6;26;36) of a medium for treating liquid, the medium in the second holder including an ion exchange material loaded with at least a second counter ion species of the same polarity as the first, wherein the media in the first and second holders (5,6;25,26;35,36) are configured to exchange at least one of the first and second counter ion species for ions in the liquid to a different extent, wherein at least one of the medium in the first holder (5;25;35) and the medium in the second holder (6;26;36) includes an amount of cation exchange material in the hydrogen form, wherein the system is arranged to lead a first fraction of the liquid to be treated through only the first of the first and second holders (5,6;25,26;35,36) and a second fraction of the liquid to be treated through at least the second of the first and second holders (5,6;25,26;35,36), and wherein the system comprises a replaceable cartridge having a housing in which the first and second holders (5,6;25,26) are arranged or comprises at least two replaceable cartridges (35,36), each including a respective housing, in which the first and second holders are respectively arranged, characterised in that the ion exchange material included in the media in the first and second holders (5,6;25,26;35,36) is a weakly acidic cation exchange polymer, and in that the system is arranged to lead at least a third fraction of the liquid to be treated through neither of the first and second holders (5,6), but through a bypass conduit containing no ion exchange material or an ion exchange material for ion species of opposite polarity to the first and second counter ion species. a first holder (5;25;35) of a medium for treating liquid, the medium in the first holder (5;25;35) including an ion exchange material loaded with at least a first counter ion species; and a second holder (6;26;36) of a medium for treating liquid, the medium in the second holder including an ion exchange material loaded with at least a second counter ion species of the same polarity as the first, wherein the media in the first and second holders (5,6;25,26;35,36) are configured to exchange at least one of the first and second counter ion species for ions in the liquid to a different extent, wherein at least one of the medium in the first holder (5;25;35) and the medium in the second holder (6;26;36) includes an amount of cation exchange material in the hydrogen form, wherein the system is arranged to lead a first fraction of the liquid to be treated through only the first of the first and second holders (5,6;25,26;35,36) and a second fraction of the liquid to be treated through at least the second of the first and second holders (5,6;25,26;35,36), and wherein the system comprises a replaceable cartridge having a housing in which the first and second holders (5,6;25,26) are arranged or comprises at least two replaceable cartridges (35,36), each including a respective housing, in which the first and second holders are respectively arranged, characterised in that the ion exchange material included in the media in the first and second holders (5,6;25,26;35,36) is a weakly acidic cation exchange polymer, and in that the system is arranged to lead at least a third fraction of the liquid to be treated through neither of the first and second holders (5,6), but through a bypass conduit containing no ion exchange material or an ion exchange material for ion species of opposite polarity to the first and second counter ion species.