In the Vishnu temples theertha Prasad is offered and thereafter sadari is kept. Some archakas say do not apply the theertha after consuming because sadari is kept on the head which is Nammalwar [sadagopan]. If we apply the remaining theertha it is like abusing sadari as our salaiva also will go on our head with the left out small pinch of theertha. But in big temples like Ranganathaswamy temple of srirangam they will not say this. Any puranic evidence for this.