On my last batch of vodka I cut my alcohol with some store bought 'pure spring water'. At first I thought it was a really good clean product, but after a couple of weeks I noticed my neutral wasn't so neutral. Would this be the alcohol reacting with the minerals in the water? Looking at the water for example, it has some sodium in it (0.5mg/200ml) which I'm guessing would react with the alcohol?
Previous to this I have been using filtered water from the tap. On my next run I will cut it with distilled water from the supermarket.