How do balanced chemical equations show the conservation of mass?

You cannot create something from nothing and similarly you cannot create less from more, if you didn't balance an equation that needs to be balanced, your product might end up equalling more or less than the total mass of the two elements combined. Which is impossible

a saline water is fed to a reverse osmosis unit at flow rate o rotameter connected to reject (retentate) line reads 8 installed in reject and permeate line reads 15.2 milli siemens/cm and 300 micro siemens/com respectively.