unless explicitly stated something else , the following description refers to the process depicted in fig1 as well as to the process depicted in fig2 . for treatment , in particular pretreatment , the water , typically decationized water , is passed through an inlet 102 of a counter - current ion exchange unit 100 including a weak base anion exchange bed 110 , a first strong base anion exchange bed 120 and a second strong base anion exchange bed 130 . within the counter - current ion exchange unit 100 , the anion exchange beds 110 ; 120 ; 130 are connected in series , wherein the weak base anion exchange bed 110 is directly arranged upstream of the first strong base anion exchange bed 120 and the first strong base anion exchange bed 120 is directly arranged upstream of the second strong base anion exchange bed 130 . thus , the water to be treated passes the anion exchange beds in the sequence of the weak base anion exchange bed 110 , the first strong base anion exchange bed 120 and the second strong base anion exchange bed 130 ( as illustrated by the arrowhead ). during passage of the weak base anion exchange bed 110 , the water is mainly freed from mineral acids and organics . during passage of the first strong base anion exchange bed 120 , the water is mainly freed from silica and carbon dioxide . depending on the resin used for the first strong base anion exchange bed 120 , toc may be removed in addition by that exchange bed . since boron is typically the first impurity ( or at least one of the first impurities ) that breaks through a strong base anion exchange bed , the water is mainly freed from boron when passing the second strong base anion exchange bed 130 . depending on the resin used for the second strong base anion exchange bed 130 , toc may be additionally removed by that exchange bed . in case of the process principle as depicted in fig1 , between the weak base anion exchange bed 110 and the first strong base anion exchange bed 120 , in particular at the outlet of the bed 110 , an inert resin layer 114 may be arranged . furthermore , between the first strong base anion exchange bed 120 and the second strong base anion exchange bed 130 , in particular at the outlet of the bed 120 , an inert resin layer 124 may be arranged . moreover , between the second strong base anion exchange bed 130 and the outlet 106 of the counter - current ion exchange unit 100 , in particular at the outlet of the bed 130 , an inert resin layer 134 may be arranged . the resin layer 134 advantageously prevents the outlet 106 from being blocked with resin material of the second strong base anion exchange bed 130 . furthermore , the resin layer 134 facilitates a more homogenous distribution of a regeneration solution such as sodium hydroxide solution within the anion exchange beds 130 ; 120 ; 110 during a downflow regeneration process such as depicted in fig1 b . in case of the process principle as depicted in fig2 , between the inlet 102 of the counter - current ion exchange unit 100 and the weak base anion exchange bed 110 , in particular at the inlet of the bed 110 , an inert resin layer 114 may be arranged in order to facilitate a more homogenous distribution of the water to be treated within the counter - current ion exchange unit 100 . this inert resin layer 114 prevents also the top nozzles of the bed 110 to be blocked with resin beads or resin fines during the upflow regeneration . furthermore , between the weak base anion exchange bed 110 and the first strong base anion exchange bed 120 , in particular at the inlet of the bed 120 , an inert resin layer 124 may be arranged in order to facilitate a more homogenous distribution of the water to be treated within the counter - current ion exchange unit 100 . this resin layer 124 prevents also the top nozzles of the bed 120 to be blocked with resin beads or resin fines during the upflow regeneration process . moreover , between the first strong base anion exchange bed 120 and the second strong base anion exchange bed 130 , in particular at the inlet of the bed 130 , an inert resin layer 134 may be arranged in order to facilitate a more homogenous distribution of the water to be treated within the counter - current ion exchange unit 100 . this resin layer 134 prevents also the top nozzles of the bed 130 to be blocked with resin beads or resin fines during the upflow regeneration process such as depicted in fig2 b . the water exiting the outlet 106 of the counter - current ion exchange unit 100 preferably has a boron concentration below 100 ppt ( parts per trillion ) and may be passed through subsequent treatment sections such as a make - up section and / or a polishing section . in particular , it may be within the scope of the invention that the water exiting the counter - current ion exchange unit 100 is passed through further treatment units such as degassing units , deionizing units , uv treating units , ultrafiltration units , reverse osmosis units , or the like . the first strong base anion exchange bed 120 , in particular an outlet thereof , is preferably connected to a silicon analyzer 140 ( preferably a dissolved silica analyzer ) via a silica sampling line 145 . when the first strong base anion exchange bed 120 becomes exhausted and the measured silica concentration exceeds a defined concentration , preferably a concentration of 20 ppb ( parts per billion ), the treating process is interrupted and the anion exchange beds 130 ; 120 ; 110 are regenerated in series ( thoroughfare regeneration ) in a counter - current modus , i . e . in the sequence of the second strong base anion exchange bed 130 , the first strong base anion exchange bed 120 and the weak base anion exchange bed 110 , as shown in fig1 b and fig2 b ( and illustrated by the arrowhead ). for regeneration of the anion exchange beds 130 ; 120 ; 110 , the counter - current ion exchange unit 100 is typically fed with a regeneration solution , preferably a warm sodium hydroxide solution , via the outlet 106 . further , an outlet of the second strong base anion exchange bed 130 is preferably connected to a boron analyzer 150 via a boron sampling line 155 . for being able to monitor boron concentration in an operational state of the treatment process , the boron analyzer 150 may require a resistivity of the sample water above 15 mohm · cm . to this end , a strong acid cation exchange bed 160 , typically being configured as a small column , may be arranged between the boron analyzer 150 and the outlet of the second strong base anion exchange bed 130 . the strong acid cation exchange bed 160 increases resistivity by exchanging protons ( h + - ions ) against sodium cations exiting the second strong base anion exchange bed 130 . when the second strong base anion exchange bed 130 becomes exhausted and the boron breakthrough and elution , respectively from the second strong base anion exchange bed 130 exceeds a defined concentration , preferably a concentration of 100 ppt ( parts per trillion ), the treating process is also interrupted and the anion exchange beds 130 ; 120 ; 110 are also regenerated in series in a counter - current mode , as shown in fig1 b and fig2 b ( and illustrated by the arrowhead ). in summary , a significant reduction of boron leakage can be accomplished by arranging a further strong base anion exchange bed ( directly downstream ) of a first strong base anion exchange bed , with the further strong base anion exchange bed being primarily provided for removing boron displaced by an impurity front , in particular silica front . in order to further minimize boron leakage , silica concentration upstream of the further strong base anion exchange bed and / or boron concentration downstream of the further strong base anion exchange bed can be monitored and the anion exchange beds can be regenerated in series in a counter - current mode when the silica and / or boron concentration exceeds defined threshold values , preferably as disclosed in the present description . by doing so , the further strong base anion exchange bed is primarily loaded with boron and is concurrently kept in a highly regenerated state .