I live in the SW and my TDS here at home is 150-200'ish.  Ive always used tap water - no issues that I know of.  I recently was given a RODI system and will be installing it when time permits.   
 
I'll run with it for a few months and see how my main tank responds...  
 
I am guessing that there will be nothing noticeable.  However, if there was ever a problem with the water you'd never notice if your running RODI. 
 
Its that 1-2% chance. 
		
	
		
		
		
		
		
	
		
		
	
	
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