A method for determining the silica concentration and the TOC concentration at the end of a full desalination line, comprising the steps of: a) providing the full desalination line comprising at least one ion exchange system, wherein the ion exchange system comprises at least one cation exchange stage and at least one anion exchange stage; b) operating the full desalination line by passing a solution to be desalinated through the ion exchange system; c) measuring n pH values pH 1 to pH n of the solution after the anion exchange stage during the operation of the full desalination line at different times t 1 to t n; d) calculating a mean value pH averaged from the pH values pH 1 to pH n; e) measuring a current pH value pH n+1 at a time t n+1, wherein the time t n+1 is after the time t n; f) calculating a pH difference ΔpH between the mean value pH averaged and the current pH value pH n+1 after ΔpH = pH averaged - pH n+1; and g) determining the silica concentration after the anion exchange stage of the full desalination line and the TOC concentration after the anion exchange stage of the full desalination line from the pH difference ΔpH; wherein the determining in step g) is according to the following formula c SiO 2 + TOC = B + K ⋅ 10 Δ pH − 1 wherein c (SiO2+TOC) is the total concentration of silica and TOC after the anion exchange stage in ppb; B is from 0.01 to 20 ppb; K is from 30 to 200 ppb; and the method further comprises a step of calibrating a meter used for measuring the pH values, wherein the calibrating is in a time period between a time t 0 and the time t 1, wherein t 0 is a time that is after the start of the operation of the full desalination line and a time period between the start of the operation of the full desalination line and t 0 is about 5% of the total time of the operation of the full desalination line; and a time period between the start of the operation of the full desalination line and t 1 is about 10% of the total time of the operation of the full desalination line. a) providing the full desalination line comprising at least one ion exchange system, wherein the ion exchange system comprises at least one cation exchange stage and at least one anion exchange stage; b) operating the full desalination line by passing a solution to be desalinated through the ion exchange system; c) measuring n pH values pH 1 to pH n of the solution after the anion exchange stage during the operation of the full desalination line at different times t 1 to t n; d) calculating a mean value pH averaged from the pH values pH 1 to pH n; e) measuring a current pH value pH n+1 at a time t n+1, wherein the time t n+1 is after the time t n; f) calculating a pH difference ΔpH between the mean value pH averaged and the current pH value pH n+1 after ΔpH = pH averaged - pH n+1; and g) determining the silica concentration after the anion exchange stage of the full desalination line and the TOC concentration after the anion exchange stage of the full desalination line from the pH difference ΔpH; the determining in step g) is according to the following formula c SiO 2 + TOC = B + K ⋅ 10 Δ pH − 1 wherein c (SiO2+TOC) is the total concentration of silica and TOC after the anion exchange stage in ppb; B is from 0.01 to 20 ppb; K is from 30 to 200 ppb; and the method further comprises a step of calibrating a meter used for measuring the pH values, wherein the calibrating is in a time period between a time t 0 and the time t 1, wherein t 0 is a time that is after the start of the operation of the full desalination line and a time period between the start of the operation of the full desalination line and t 0 is about 5% of the total time of the operation of the full desalination line; and a time period between the start of the operation of the full desalination line and t 1 is about 10% of the total time of the operation of the full desalination line.