Pivot table relative percentage

[#1]

Here in this pivot table for the field volume i have written the expression

=if(Dimensionality()=0,

  Sum(Aggr(sum(Query3.Volume),Query3.Water_System,Query2.REGION,MonthName)),

   if(Dimensionality()=1,

     Sum(Aggr(sum(Query3.Volume),Query3.Water_System,MonthName))

  ))