I'm showing 0 TDS out of my membrane (I have good tap water). Does the DI remove other impurities that don't measure as TDS or am I running through DI for no reason? TDS out of my faucet is between 10 and 15 if it matters. My current RO/DI system (6 stage) is a bit overkill for the water here - I bought it when I lived in Arizona. The TDS out of the tap there was reading over 500.