3. In so far as particulars of any of the anions, cations, non–ionised compounds or trace elements specified in column 1 of Schedule 5 are required to be given pursuant to sub–paragraph (b) of paragraph 2, the concentration of each such anion, cation, non–ionised compound or trace element shall be expressed in those particulars in the unit of measurement specified opposite to it in column 2 of that Schedule.